DOCSLIB.ORG

Stereoselective Transformations Starting with Chiral (Aikoxy)Methyl-Substituted Organosilicon Compounds

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Stereoselective Transformations Starting with Chiral (Aikoxy)Methyl-Substituted Organosilicon Compounds AWARDS 1996 (NSCS) . PREISTRAGER 1996 (NSCG) 133 CHIMIA 5/ (1997) Nr. 4lApriIJ A a 1996 ( rager•• Chimia 51 (/997) 133-139 © Neue Schweizerische Chemische Gesellschaft ISSN 0009-4293 Stereoselective Transformations Starting with Chiral (AIkoxy)methyl-Substituted Organosilicon Compounds Stefan Bienz* Stefan Bienz was born on Januar 17, 1958, in (Werner Prize 1996 of the NSCS) Lucerne (CH). He is citizen ofWolhusen (LU) and Lucerne, Switzerland. Academic Background: 1977-1983: Studies Abstract. The following short review summarizes the results we achieved with the in Chemistry at the Phi losophical Faculty II of investigation of chiral silicon groups as auxiliaries for the enantioselective synthesis. the University of Zurich, Switzerland. Gradu- (Alkoxy)methyl-substituted silicon compounds with 'Si-centered chirality', which ate research under the supervision of Prof. Dr. were prepared in optically active form by application of a bioreduction, have been M. Hesse at the Institute of Organic Chemistry towards the diploma (May 5, 1983; thesis: efficiently used as starting materials for a number of stereoselective reactions. Acylsi- 'Contribution to the Transformation of Car- lanes of this type upon treatment with organometallic reagents gave rise to 1,2-addition bocycIes to Lactams by Ring Enlargement products with high degrees of stereoselectivities. The respective a-hydroxysilanes Reaction') and 1983-1987 towards the Ph.D. could be stereospecifically desilylated to chiral secondary alcohols, or, depending on (December 18, 1987; thesis: 'Synthesis of the substitution pattern, further used as starting compounds for stereocontrolled Macrocyc\ic Natural Products by Ring En- oxidation, Cope- or Claisen-type rearrangement reactions. Chiral a-metallated vinyl- largement Reactions', distinguished for its silanes were converted to a-silyl-substituted allylic alcohols and to a-silyl-substituted excellence). 1988-1989: Postdoctoral studies at the Colo- a,j3-unsaturated ketones. The prior led to chiral allenes in a Peterson-type reaction - rado State University, Fort Collins, Colorado however, without stereoselectivity - the latter delivered stereoselectively j3-chiral (USA) with Prof. Dr. A. I. Meyers in the field silicon-free ketones upon stereocontrolled conjugate cuprate addition followed by of enantioselective synthesis. removal of the silicon auxiliary. Since 1990 at the Institute of Organic Chem- istry, University of ZUrich, Switzerland: Head assistant and lecturer; Summer 1995: Venia legendi (habilitation treatise: 'Enantioselec- 1. Introduction silanes 1that gave in highly enantioselec- tive Synthesis Using Amino Acid or Silicon tive allylation reactions rise to a variety of Based Chiral Auxiliaries and Synthesis of Organosilicon chemistry has undergone a compounds [5][6]. The chiral allylsilanes Polyamine Toxins from Spiders and Wasps'). tremendous development over the last two 1,however, do not possess a 'chiral silicon Research interests: stereoselective synthesis or three decades. It is fair to state that moiety' which delivers stereochemical in- with organosilicon compounds, synthetic rel- nowadays, the majority of multistep or- formation onto a carbon framework; the evant mass spectrometric methods and frag- ganic syntheses makes use of organosili- stereochemical information is already mentations, unusual substrates for bio- transformations, physiologically interesting con compounds in one way or another: as stored on the reactive group, which itself polyamine conjugates. reagents for C,C-bond formations, forfunc- is attached to an 'achiral silicon group' tional-group transformations, or for func- (silanes of the type A with 'proximate C- tional-group protections. With the advanc- centered chirality' [4]). Transfer of chiral- attained in several transformations with ing interest in the preparation of enantio- ity from a chiral silicon auxiliary to a proline-derivedchiral silanes 2 (that are of merically pure compounds, it is not sur- neighboring prostereogenic group, how- the type B) [2]. The scope of reactions prising that also attention has been in- ever, has been realized with silanes ofthe with this type of substrates, however, is creasingly directed towards stereoselec- type Band C. These compounds have limited, since no common chiral silicon tiveprocesses involvingchiral silicon com- located the chirality either on an inert side precursor (like, e.g., a chlorosilane) is pounds [1-6]. Some rather impressive re- chain (compounds of the type B with 're- employed. So far, only little use of chiral sults were obtained, e.g., with chiral allyl- mote C-centered chirality') or- in form of silicon compounds of the type C has been a stereogenic center - on silicon itself made for the enantioselective synthesis (compounds of the type C with 'Si-cen- [1-5]. This is probably due to the low *Correspondence: PO Dr. S. Bienz tered chirality' [4]). It is just astonishing, stereoselectivities that were obtained in Organisch-chemisches Institut Universitiit ZUrich though, how little work has been per- several reactions where almost exclusi ve- Winterthurerstrasse J 90 formed with such substrates. Some re- Iy derivatives of 3 have been used as the CH-8057 ZUrich markable stereoselectivities were lately chiral starting compounds. AWARDS 1996 (NSCS) . PREISTRAGER 1996 (NSCG) 134 CHIMIA 5/ (1997) Nr. 4 (April) Enhanced stereoselectivities were ex- external prostereogenic electrophiles, re- alents, followed by the respective func- pected to be attained, if (alkoxy)methyl- spectively, leading to novel chiral com- tional-group interconversion. They were substituted chiral silanes 4 were used in- pounds amenable to further transforma- alternatively transferred into (a-iodovi- stead of derivatives of3. These compounds tions. nyl)silanes 10 (the ultimate precursors of should be enabled to form cyclic chelate a-metallated vinylsilanes 6) by treatment intermediates or transition states with cat- with a suitable lithium acetylide, reduc- ionic additives (metals, M). As a conse- 2. Preparation of Chiral tion of the obtained alkynylsilanes 9 with quence of the rigid intermediary structure, (Alkoxy)methyl-Substituted Silanes diisobutylaluminum hydride (OIBAR), they should effect an improved discrimi- and quenching of the resultant vinylalane nation of the different spatial approaches Racemic chiral (alkoxy)methyl-substi- with iodine [8]. The stereochemistry of the reacting species. This is in fact tuted silanes were prepared straightfor- around the C=C bond of 10 can be control- observed, as will be shown in this short wardly from commercial (chloromethyl)- led by the proper choice of the reduction review: below, we describe the prepara- dichloro(methyl)silane (7) [7]: Stepwise conditions; for (E)-configurated silanes tion of chiral (benzyloxy)methyl-substi- substitution of the Cl-atoms (via bis(ben- 10, the C=C bond geometry can also be tuted silanes and some subsequent stereo- zyloxy)silane intermediates) - first at the inverted in the course of the subsequent selective transformations. Focus will be chloromethyl group with the benzyloxy metallation step. directed on the primary and subsequent residue, then at the silicon center with the Optically active acylsilanes 5 are ac- reactions of two types of chiral organosil- tert-butyl group - provided the racemic cessible by using a biotransformation step: icon compounds, namely acylsilanes 5 chlorosilane 8 (Scheme 1), which could be e.g., (±)-5a is recognized by several mi- and a-metallated vinylsilanes 6. These used as the common precursor for the croorganisms as a substrate and is reduced substrates should stereoselectively react synthesis of a variety of silanes. Com- stereospecifically to the corresponding a- either as electrophiles at the prostereogen- pound 8 was thus converted into acylsi- hydroxysilanes (+)-(SiR,R)-lla and (+)- ic carbonyl group or as nucleophiles with lanes 5 by reaction with acyl-anion equiv- (SiS,R)-lla' (Scheme 2) [9][10]. These diastereomeric alcohols were separated by chromatography and reoxidized to (-)- R (R)-5a and (+)-(S)-5a, respectively. Alter- I natively, the two alcohols can be convert- R-Si~R" MeI - Type A I e.g. r=<,R' 1 ed to the hydrosilanes (+)-(S)-12a and R Me-~i"" Rz Chiral Reactive Group Me R (-)-(R)-12a by treatment with KH (Brook rearrangement [11][12]) and reduction of ('Proximate C-Centered Chirality') the thus obtained silyl ethers with LiAlH4 [13]. Best results in the biotransformation R* r step were obtained with immobilized rest- R-Si-Reeae ing cells of Trigonopsis variabilis (DSM Type B I e.g. ("'={OMe 2 R 70714), which provided the desired prod- Me-SI-Reeae Chirallnert Substituent I ucts not only in high chemical yields and Me with enantiomeric excesses > 96%, but ('Remote C-Centered Chirality') also allowed to develop a handy workup procedure. R1 I . Ph 2 R -ShReeae 1.* Type C e.g. a.-Npht- SI-Rreae 3 R3 I 3. Stereoselective Reactions Starting Chiral Silicon Center Me with Chiral Acylsilanes ('Si-Centered Chirality') 3.1. 1,2-Addition to the Carbonyl Group The 1,2-addition of organometallic re- Bn I agents to the carbonyl group of acylsilanes 0, 5 afforded the respective addition prod- ( '¥ .. ucts 13 with varying degrees of diastereo- Me""Si 6 selectivity [7][14] (Scheme 3, shown ex- Mej( r: emplary for the conversion of (-)-(R)-5a R Me R''---. I Me \ to (+)-(SiR,R)-13a). Particularly high se- 0, lectivities were attained, when the reac- ( 'M 5 prostereogenic tions were carried out in nonbasic sol- Me....:./Me""Si "R " vents, like, e.g., hexane
Load more

Recommended publications
  • Computational and Experimental Evidence on Reaction Mechanisms of Oxidized Sulfur-Containing Compounds in Ground and Excited States Jerry W
    Iowa State University Capstones, Theses and Retrospective Theses and Dissertations Dissertations 2001 Computational and experimental evidence on reaction mechanisms of oxidized sulfur-containing compounds in ground and excited states Jerry W. Cubbage Iowa State University Follow this and additional works at: https://lib.dr.iastate.edu/rtd Part of the Organic Chemistry Commons, and the Physical Chemistry Commons Recommended Citation Cubbage, Jerry W., "Computational and experimental evidence on reaction mechanisms of oxidized sulfur-containing compounds in ground and excited states " (2001). Retrospective Theses and Dissertations. 419. https://lib.dr.iastate.edu/rtd/419 This Dissertation is brought to you for free and open access by the Iowa State University Capstones, Theses and Dissertations at Iowa State University Digital Repository. It has been accepted for inclusion in Retrospective Theses and Dissertations by an authorized administrator of Iowa State University Digital Repository. For more information, please contact [email protected]. INFORMATION TO USERS This manuscript has been reproduced from the microfilm master. UMI films the text directly from the original or copy submitted. Thus, some thesis and dissertation copies are in typewriter face, while others may be from any type of computer printer. The quality of this reproduction is dependent upon the quality of the copy submitted. Broken or indistinct print, colored or poor quality illustrations and photographs, print bleedthrough, substandard margins, and improper alignment can adversely affect reproduction. In the unlikely event that the author did not send UMI a complete manuscript and there are missing pages, these will be noted. Also, if unauthorized copyright material had to be removed, a note will indicate the deletion.
    [Show full text]
  • 5-Endo-Die. Approaches to Pyrroles Jirada Singkhonrat
    5-Endo-Die. Approaches to Pyrroles A thesis submitted to Cardiff University By Jirada Singkhonrat BSc, MSc In candidature of Doctor of Philosophy September 2004 Department of Chemistry Cardiff University UMI Number: U584670 All rights reserved INFORMATION TO ALL USERS The quality of this reproduction is dependent upon the quality of the copy submitted. In the unlikely event that the author did not send a complete manuscript and there are missing pages, these will be noted. Also, if material had to be removed, a note will indicate the deletion. Dissertation Publishing UMI U584670 Published by ProQuest LLC 2013. Copyright in the Dissertation held by the Author. Microform Edition © ProQuest LLC. All rights reserved. This work is protected against unauthorized copying under Title 17, United States Code. ProQuest LLC 789 East Eisenhower Parkway P.O. Box 1346 Ann Arbor, Ml 48106-1346 Declaration This work has not previously been accepted in substance for any degree and is not being concurrently submitted in candidature for any degree. Signed a toJfl (candidate) Date QS_____________ Statement one This thesis is the result of my own investigations, except where otherwise stated. Other sources are acknowledged by footnotes giving explicit references. A bibliography is appended. Signed vo ________ (candidate) Date k y ja * } Q 5__ Statement two I hereby give consent for my thesis, if accepted, to be made available for photocopying and for inter-library loan, and for the title and summary to be made available to outside organisations. Signed — aofg errs (candidate) Date wJXv* 0 5 Abstract This project required developing new practical routes towards pyrroles and could help the project of total synthesis of (-)-rhazinilam.
    [Show full text]
  • Copyrighted Material
    JWST960-SUBIND JWST960-Smith October 25, 2019 9:5 Printer Name: Trim: 254mm × 178mm SUBJECT INDEX The vast use of transition metal catalysts in organic chemistry makes the citation of every individual metal impractical, so there are limited citations of individual metals. Palladium is one exception where individual citations are common, in keeping with the widespread use of that metal. However, in most cases, the term metal catalyst, or catalyst, metal is used as a heading, usually representing transition metals. A-SE2 mechanism 893 and the steering wheel model acceleration of Diels-Alder reactions 487 151–152 reactions, high pressure A1 mechanism, acetal hydrolysis and universal NMR database 1038 487 155 hydrogen-bonding 1038 A1,3-strain 196 Cahn-Ingold-Prelog system hydrophobic effect 1038 A2 mechanism, acetal hydrolysis 149–152 in water 1038 487 determination 152 ionic liquids 1038 ab initio calculations 36 D/L nomenclature 149 micellular effects 1038 and acidity 346 Kishi’s NMR method 155 microwave irradiation 1038 and antiaromaticity 71 sequence rules 149–152 phosphate 1039 and nonclassical carbocations absolute hardness 64, 359, 361 solid state 1038 427 table 361 ultracentrifuge 1038 norbornyl carbocation 436 absorbents, chiral 168 ultrasound 1038 ab initio studies 248 absorption, and conjugation 317 zeolites 1038 1,2-alkyl shifts in alkyne anions differential, and diastereomers acceleration, Petasis reaction 1349 168 1202 and cubyl carbocation 413 differential, and resolution 169 acenaphthylene, reaction with and SN2 408–409 abstraction,
    [Show full text]
  • Introductory Reaction Mechanism
    GOC-III(Introductory Reaction Mechanism) Introductory Mechanisms in Organic Reactions A reaction mechanism is a step by step narration of the bond-breaking and bond-making processes that occur when reagents react to form the products. The proof of the mechanism, that the reaction is really going via this route, not via the other route, has been established by many experimental corroborations. Let us study the mechanisms of several organic reactions. Substitution Reactions: Substitution reactions are of three types (a) Free Radical Substitution (SF) (b) Nucleophilic Substituion(SN) (c) Electrophilic Substituion(SE) Free Radical Substitution(SF) Usually alkanes or alkenes undergo free radical substitution at the sp3 hybrid carbon, where a stable carbon free radical is formed. For introductory purpose we take halogenation of alkane in presence of heat and light for explaining SF mechanism. light/heat R H + X2 R X + HX A H atom in alkane is substituted by a halogen atom (X) when alkane reacts with halogen in presence of uv/visible light or heat or both. This reaction proceeds with the participation of free radicals(not any ionic species) and hence its name SF. A free radical mechanism proceeds via the following three steps (i) Initiation (ii) Propagation (iii) Termination Alkane reacts with halogen like Cl2 and Br2(written as X2) in the vapour phase in presence of light or heat to produce haloalkane(alkyl halide) This reaction goes via the above three steps. Let us discuss one by one. Initiation: light/heat XX 2 X The reagent X2 undergoes homolytic cleavage of the bond in presence of light or heat or both to produce two halogen free radicals(better call them atoms).
    [Show full text]
  • Β-Elimination Reaction of Antimicrobial L-5-Alk (En
    Agric. Biol. Chem., 43 (10), 2017-2020, 1979 2017 ƒÀ-Elimination Reaction of Antimicrobial L-5-Alk(en)yl- thiomethylhydantoin-S-oxides Satoshi TAHARA, Hiroyuki OKAMURA, YUZO MIURA and Junya MIZUTANI Department of Agricultural Chemistry , Faculty of Agriculture, Hokkaido University, Sapporo 060, Japan Received July 19, 1978 The antimicrobial L-5-alk(en)ylthiomethylhydantoin-(•})-S-oxides (RHSO) decompose spontaneously via ƒÀ-elimination under physiological conditions to give 5-methylenehydantoin and alk(en)yl thiosulfinates as antimicrobial principles. Attempts have been made to elucidate the mechanism of ƒÀ-elimination reaction of RHSO in a buffer solution. The ƒÀ-elimination of propyl derivative (I) at specified conditions of temperature and pH followed first-order kinetics. A linear relationship between the first-order rate constant and the concentration of hydroxide ion was also observed. Therefore, it has been shown that the ƒÀ-elimination of I obeys the second-order kinetics. The second-order rate constant from L-5-propylthiomethylhydantoin- (+)-S-oxide [(+)-I] in water at 37•Ž was 4.20•}0.31•~103/sec. M. As shown in our previous papers,1,2) the L- fore, the ƒÀ-elimination reactions of two dia- 5-alk(en)ylthiomethylhydantoin- (•})-S- oxides stereoisomeric substrates, (+)-I and (-)-I (RHSO) decomposed via a ƒÀ-elimination re were carried out in a buffer solution at 37•Ž. action under physiological conditions to give As shown in Table II, nearly constant values 5-methylenehydantoin and highly antimicro were obtained by the calculation using the bial alk(en)yl thiosulfinates. In this paper, experimental results according to the equation we deal with L-5-propylthiomethylhydantoin- for first-order kinetics (k=l/t In 100/(100-ƒÔ)).
    [Show full text]
  • Types of Organic Reaction Mechanisms Module Tag CHE P5 M2
    ____________________________________________________________________________________________________ Subject Chemistry Paper No and Title Paper No. 5:Organic Chemistry-II Module No and Title Module No. 2: Overview of different types of Organic Reaction Mechanisms Module Tag CHE_P5_M2 CHEMISTRY PAPER No. 5: REACTION MECHANISM MODULE No. 2: Types of Organic Reaction Mechanisms ____________________________________________________________________________________________________ TABLE OF CONTENTS 1. Learning Outcomes 2. Introduction 3.Types of Reaction Mechanisms 3.1 Substitution Nucleophilic Unimolecular Mechanism (SN1) 3.2 Substitution Nucleophilic Bimolecular Mechanism (SN2) 3.3 Substitution Nucleophilic Internal Mechanism (SNi) 3.4 Aromatic Nucleophilic substitution mechanism (SNAr) 3.5 Substitution Radical Nucleophilic Unimolecular(SRN1) 3.6 Electrophilic Aromatic Substitution Mechanism (EAS) 3.7 Unimolecular Elimination Mechanism (E1) 3.8 Bimolecular Elimination Mechanism (E2) 3.9 Conjugate Base Elimination Mechanism (E1cb) 3.10 Elimination Internal Mechanism (Ei) 3.11 Free Radical Mechanism 3.12 Concerted Mechanism 4. Summary CHEMISTRY PAPER No. 5: REACTION MECHANISM MODULE No. 2: Types of Organic Reaction Mechanisms ____________________________________________________________________________________________________ 1. Learning Outcomes After studying this module, you shall be able to: • Know how organic reactions proceed. • Identify the different types of reaction mechanisms. • Analyse the difference between each type of mechanism. 2. Introduction Reaction Mechanism: Mechanism for any reaction is defined as collection of number of processes that explains the overall reaction. • This is the actual method of completion of reaction as it gives the number of broken bonds and the number of steps involved. • In a mechanism thepositions of all atoms (stereochemistry), role of solvent molecules and the energy of thesystem is specified. • It also helps in describing the reaction intermediate, activated complex and transition state involved in the whole reaction.
    [Show full text]
  • And Trans-5, 5-Dimethyl-1, 3-Cyclohexanediol Bis-P
    Kinetics and Mechanism of the Solvolysis of cis- and trans-5,5-Dimethyl-1,J-cyclohexanediol Bis-~-toluenesulfonate in Aqueous Pyridine A Thesis Presented to the Faculty of the Sciences and Mathematics School Morehead State University In Partial Fulfillment of the Requirements for the Degree Master of Science in Chemistry by Louis Frederick Holzknecht May 1977 AP r'·l'\ ' I I"-.., __ ;,,- 1 /. - H'lb'J t, Accepted by the faculty of the School of Sciences and Mathematics, Morehead State University, in partial fulfillment of the requirements for the Master of Science degree . Master's Committee: Kinetics and Mechanism of the Solvolysis of cis- ~nd trans-5,5-Dimethyl-1,J-cyclohexanediol Bis-~-toluenesulfonate in Aqueous Pyridine Louis Frederick Holzknecht, M,S, Morehead State University, 1977 Director of Thesis: Dr, Lamar B, Payne Alkyl substituted and unsubstituted mono and bis­ arenesulfonates have been previously shown to undergo a retro Prins-like rearrangement in basic media. It was of interest to determine if this type of rearrangement extended to cis- and trans-5,5-dimethyl-1,J-cyclohexanediol bis-~­ toluenesulfonate,.and whether the rearrangement might be initiated by the Lewis base pyridine, The solvolyses of the cis- and trans-bistosylates in aqueous.-pyridine..: o.bey.e.cl..-pseudo.- f.irst~order -kinetics~. Typically,- rate differences-between the··-two -isomeric--bis­ tosylates solvolyzing at equal temperatures were on the order of 4-5 favoring the trans-bistosylate, Increasing the water concentration in the solvolysis medium resulted in a directly proportional increase in the reaction rate of the solvolysis, Calculation of thermodynamic parameters for the solvolyses of the bistosylates in 80% aqueous pyridine yielded the following data at 90°c, cis­ bistosylate, b.H*= 24,48 kcal/mole, b.s*= -12,J e,u,; trans-bistosylate, ~H*= 22.38 kcal/mole, ~s*= -14.9 e.u.
    [Show full text]
  • Structure and Mechanism of the Formylglycine-Generating Enzyme
    Structure and Mechanism of the Formylglycine-generating Enzyme By Mason J. Appel A dissertation submitted in partial satisfaction of the requirements for the degree of Doctor of Philosophy in Molecular and Cell Biology in the Graduate Division of the University of California, Berkeley Committee in charge: Professor Carolyn R. Bertozzi, Co-Chair Professor Judith P. Klinman, Co-Chair Professor Jack F. Kirsch Professor Matthew B. Francis Fall 2017 Structure and Mechanism of the Formylglycine-Generating Enzyme © 2017 By Mason J. Appel Abstract Structure and Mechanism of the Formylglycine-generating Enzyme By Mason J. Appel Doctor of Philosophy in Molecular and Cell Biology University of California, Berkeley Professor Carolyn R. Bertozzi, Co-Chair Professor Judith P. Klinman, Co-Chair The ability of enzymes to make rapid the conversion between chemical entities represents an enabling feature for life. The strategies by which enzymes achieve this feat are manifold in their details and physiological consequences. Though the central importance of biological catalysis has been known for well over a century, the true breadth of enzyme function is still beginning to be appreciated. A fundamental description of enzyme catalysis is essential to understanding biological processes, and is also necessary in order to realize the promise of engineered enzymes for transforming medicine and manufacturing. The formylglycine-generating enzyme (FGE) is responsible for activating sulfatase enzymes in aerobic organisms by catalyzing the post-translational modification of a cysteine residue to formylglycine. Formylglycine permits sulfatase activity by acting as a covalent cofactor. Thus, the diverse roles of sulfatases in both animal and microbial biology underscore the importance of FGE.
    [Show full text]
  • A New Mechanism for Internal Nucleophilic Substitution Reactions
    Document downloaded from: http://hdl.handle.net/10251/108670 This paper must be cited as: Aurell, MJ.; González-Cardenete, MA.; Zaragoza, RJ. (2018). A new mechanism for internal nucleophilic substitution reactions. Organic & Biomolecular Chemistry. 16(7):1101-1112. doi:10.1039/c7ob02994b The final publication is available at https://doi.org/10.1039/c7ob02994b Copyright The Royal Society of Chemistry Additional Information Please do not adjust margins Journal Name ARTICLE New mechanism for internal nucleophilic substitution reactions. María J. Aurell, a Miguel A. González-Cardenete, b and Ramón J. Zaragozá*,a Received 00th January 20xx, Accepted 00th January 20xx A new mechanism of the classic internal nucleophilic substitution reactions SNi by means of computational studies in gas-phase, DCM and acetonitrile is reported. Despite the importance of the SNi mechanism, since the mid- DOI: 10.1039/x0xx00000x 1990s this mechanism has remained unexplored. The study has focused mainly on the comparison between the www.rsc.org/ mechanisms postulated to date for the SNi reactions and a new mechanism suggested by us that fits better the experimental observations. The comparative study has been applied to the conversion of ethyl, neopentyl, isopropyl and tert-butyl chlorosulfites into the corresponding alkyl chlorides. This new mechanism occurs through two transition structures. For primary and secondary substrates, the first transition structure is a 6-center syn- rearrangement of the alkanesulfonyl chloride that produces the corresponding olefin by simultaneous expulsion of HCl and SO2. The olefin, HCl and SO2 form a molecular complex. The final syn addition of HCl to the olefin leads to the alkyl chloride with retention of configuration.
    [Show full text]
  • Burgess Reagent in Organic Synthesis†
    J. Indian Inst. Sci., July−Aug. 2001,BURGESS 81, 461–476 REAGENT IN ORGANIC SYNTHESIS 461 © Indian Institute of Science. Burgess reagent in organic synthesis† SACHIN KHAPLI, SATYAJIT DEY AND DIPAKRANJAN MAL* Department of Chemistry, Indian Institute of Technology, Kharagpur 721 302, India. email: [email protected], [email protected]; Phone: 91-3222-83318; Fax: 91-3222-755303. Received on November 29, 2000. Abstract Methyl N-(triethylammoniumsulfonyl)carbamate, also known as Burgess regent, is a mild yet powerful dehydrating agent. Usefulness of the regent in various synthetic transformations and in the synthesis of various heterocyclic systems has been reviewed. Keywords: Burgess regent, dehydrating agent, heterocycles, cyclodehydration. 1. Introduction Methyl N-(triethylammoniumsulphonyl)carbamate (1), also known as Burgess reagent,1 is a mild and selective dehydrating agent, and can be successfully utilized for the preparation of alkenes from alcohols. However, it went into oblivion for nearly a decade soon after its discovery by E. M. Burgess in 1968. It was Peter Wipf who brought it to the attention of organic chemists through its extensive use in the formation of 5-membered heterocycles from their acyclic precursors. An interesting feature of this reagent is that the dehydration is a pyrolytic reaction which can be effected below 100°C. The reagent is highly soluble in most of the common organic solvents including nonpolar ones, even though it is formulated as a salt. The dehydration takes place through a variant of Ei mechanism resulting in syn-elimination. The reagent is also known to bring about many important transformations such as preparation of isocyanides, nitriles, and nitrile oxides from formamides, primary amides and nitroalkanes, respectively.
    [Show full text]
  • Stereoselective Transformations Starting with Chiral (Aikoxy)Methyl-Substituted Organosilicon Compounds
    AWARDS 1996 (NSCS) . PREISTRAGER 1996 (NSCG) 133 CHIMIA 5/ (1997) Nr. 4lApriIJ A a 1996 ( rager•• Chimia 51 (/997) 133-139 © Neue Schweizerische Chemische Gesellschaft ISSN 0009-4293 Stereoselective Transformations Starting with Chiral (AIkoxy)methyl-Substituted Organosilicon Compounds Stefan Bienz* Stefan Bienz was born on Januar 17, 1958, in (Werner Prize 1996 of the NSCS) Lucerne (CH). He is citizen ofWolhusen (LU) and Lucerne, Switzerland. Academic Background: 1977-1983: Studies Abstract. The following short review summarizes the results we achieved with the in Chemistry at the Phi losophical Faculty II of investigation of chiral silicon groups as auxiliaries for the enantioselective synthesis. the University of Zurich, Switzerland. Gradu- (Alkoxy)methyl-substituted silicon compounds with 'Si-centered chirality', which ate research under the supervision of Prof. Dr. were prepared in optically active form by application of a bioreduction, have been M. Hesse at the Institute of Organic Chemistry towards the diploma (May 5, 1983; thesis: efficiently used as starting materials for a number of stereoselective reactions. Acylsi- 'Contribution to the Transformation of Car- lanes of this type upon treatment with organometallic reagents gave rise to 1,2-addition bocycIes to Lactams by Ring Enlargement products with high degrees of stereoselectivities. The respective a-hydroxysilanes Reaction') and 1983-1987 towards the Ph.D. could be stereospecifically desilylated to chiral secondary alcohols, or, depending on (December 18, 1987; thesis: 'Synthesis of the substitution pattern, further used as starting compounds for stereocontrolled Macrocyc\ic Natural Products by Ring En- oxidation, Cope- or Claisen-type rearrangement reactions. Chiral a-metallated vinyl- largement Reactions', distinguished for its silanes were converted to a-silyl-substituted allylic alcohols and to a-silyl-substituted excellence).
    [Show full text]
  • Totalsynthese Von Belizentrin Methylester & Ein
    Totalsynthese von Belizentrin Methylester & Ein enantiodivergenter Zugang zu chiralen Allenen Dissertation Zur Erlangung des akademischen Grades eines Doktors der Naturwissenschaften (Dr. rer. nat.) Der Fakultät für Chemie und Chemische Biologie der Technischen Universität Dortmund vorgelegt von Felix Anderl geboren am 02. 05. 1990 in Graz Mülheim an der Ruhr, den 13.12.2018 1. Berichterstatter: Prof. Dr. Alois Fürstner 2. Berichterstatter: Prof. Dr. Norbert Krause Die vorliegende Arbeit entstand unter der Anleitung von Prof. Dr. Alois Fürstner in der Zeit von Jänner 2015 bis November 2018 am Max-Planck-Institut für Kohlenforschung in Mülheim an der Ruhr. Teile dieser Arbeit wurden bereits veröffentlicht: Felix Anderl, Sylvester Größl, Conny Wirtz, Alois Fürstner: “Total Synthesis of Belizentrin Methyl Ester: Report on a Likely Conquest” Angew. Chem. Int. Ed. 2018, 57, 10712–10717; Die praktischen Arbeiten erfolgten zum Teil in Zusammenarbeit mit Dr. Sylvester Größl, Pascal Ortsack (Kapitel 4), Karin Radkowski und Dr. Macarena Corro Moron (Kapitel 5). Die beschriebenen Ergebnisse bilden eine vollständige Darstellung dieser gemeinsamen Arbeiten. Die von diesen Mitarbeitern alleinverantwortlich erzielten Ergebnisse wurden als solche an entsprechender Stelle gekennzeichnet. Danksagung: Mein größter Dank gilt Prof. Dr. Alois Fürstner, dafür dass er meine Begeisterung für die organische synthetische Chemie bestärkt hat und mir in seiner Arbeitsgruppe die Gelegenheit gegeben hat, dieses Interesse auszuleben. Ich bin ihm dankbar für interessante Aufgaben, geduldige Anleitung und viel Freiraum. Prof. Dr. Norbert Krause danke ich für die Übernahme des Koreferats dieser Arbeit. Besonders erwähnen möchte ich Prof. Dr. Christoph Marschner, Prof. Dr. Rolf Breinbauer und Dr. Mandana Gruber, die mich sehr ermutigt und unterstützt haben, um mich überhaupt zu dieser Arbeit zu bewerben.
    [Show full text]