DOCSLIB.ORG

Boronic Acids

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Boronic Acids Boronic Acids Boronic Acids www.alfa.com INCLUDING: • Boronic Esters • Oxazaborolidine Reagents • Coupling and Hydroboration Catalysts • Phosphine Ligands • Borylation Reagents www.alfa.com Where Science Meets Service Quality Boronic Acids from Alfa Aesar Alfa Aesar is known worldwide for a variety of chemical compounds used in research and development. Recognized for purity and quality, our products and brands are backed by technical and sales teams dedicated to providing you the best service possible. In this catalog, you will find details on our line of boronic acids, esters and related compounds, which are manufactured to the same exacting standards as our full offering of over 33,000 products. Also included in this catalog is a 28-page introduction to boronic acids, their properties and applications. This catalog contains only a selection of our wide range of chemicals and materials. Also included is a selection of novel coupling catalysts and ligands. Many more products, including high purity metals, analytical products, and labware are available in our main catalog or online at www.alfa.com. Table of Contents About Us _____________________________________________________________________________ II How to Order/General Information ____________________________________________________ III Introduction __________________________________________________________________________ 1 Alkenylboronic acids and esters _____________________________________________________ 29 Alkylboronic acids and esters ________________________________________________________ 33 Alkyltrifluoroborate salts______________________________________________________________ 38 Alkenyltrifluoroborate salts ___________________________________________________________ 39 Arylboronic acids ___________________________________________________________________ 39 Arylboronic esters __________________________________________________________________ 107 Aryltrifluoroborate salts _____________________________________________________________ 128 Heterocyclic boronic acids _________________________________________________________ 134 Heterocyclic boronic esters _________________________________________________________ 144 Heterocyclic trifluoroborate salts ____________________________________________________ 158 Oxazaborolidine reagents __________________________________________________________ 159 Boronation reagents ________________________________________________________________ 161 Coupling catalysts _________________________________________________________________ 164 Phosphine ligands __________________________________________________________________ 174 Non-phosphine ligands _____________________________________________________________ 179 I About Us GLOBAL INVENTORY The majority of our boronic acids and related products are available in research and development quantities from stock. We also supply most products from stock in semi-bulk or bulk quantities. Many are in regular production and are available in bulk for next day shipment. Our experience in manufacturing, sourcing and handling a wide range of metals enables us to respond quickly and efficiently to your needs. CUSTOM SYNTHESIS We offer flexible custom manufacturing serviceswith the assurance of quality and confidentiality. We can deliver the chemical you need in sizes for research, pilot-scale and full- scale production applications. CUSTOMER SERVICE Our dedicated scientific and commercial teams offer full service from production to delivery. Most products are stocked in catalog pack sizes and the majority are available from stock in semi-bulk and bulk quantities as well. All specialty and bulk products are shipped with a batch specific certificate of analysis and material safety data sheet. Because we understand that specific packaging is often important, we offer custom packaging and labeling to meet your requirements. QUALITY CONTROL We employ advanced quality control for both in-process and final product testing phases. The high standard of our modern quality control and assurance facilities is matched by the expertise of our experienced staff. II How to Order/ General Information ORDERING of your receiving the materials. Restocking fees There is no minimum order. All orders are may be charged on authorized returns. accepted, regardless of size. TERMS OF SALE PRICING Full details of Terms and Conditions are listed Most current pricing may be found at our at the back of this catalog and on our website website: www.alfa.com. In cases where the (www.alfa.com). For health and safety reasons, selling price has changed significantly, we will we shall not supply chemicals to private contact you prior to filling your web, email or individuals or deliver to residential addresses. faxed order. Our payment terms are net 30 days Orders will be accepted from legitimate business of invoice. customers only. SHIPPING NEW CUSTOMERS Whenever possible, we will ship products by the We welcome new customers and setting up an method specified on your order. account with Alfa Aesar is easy. Just call contact us and a customer service representative TECHNICAL SERVICE will assist you. At your request, we will furnish technical assistance and information with respect to our CONTACT US products. Our Technical Service Representatives WEBSITE are trained in specific product lines to answer www.alfa.com your questions regarding applications, Our webCatalysts catalog features up-to-date prices, specifications, product properties and handling. availability, MSDS, Certificates of Analysis and a user-friendly e-commerce system. MATERIAL SAFETY DATA SHEETS Each product ordered is automatically accompanied by a Material Safety Data Sheet (MSDS). If one is not immediately available, a copy will be sent via mail as soon as possible. If an MSDS is needed prior to shipment of a product please call us or visit our MSDS website at www.alfa.com/en/go160w.pgm#msds. CERTIFICATES OF ANALYSIS Lot specific Certificates of analysis are available online at www.alfa.com. Please contact us by Pilot Plant/Custom phone, fax or email to request Certificates of Analysis as needed. RETURN SHIPMENTS Some materials are not returnable. Returned shipments cannot be accepted unless prior arrangements have been made. Requests for return authorization must be made within 30 days III Abbreviations and Codes The following abbreviations are used throughout our listing of products. AAS Atomic absorption spectrometry N Normality of solution AES Atomic emission spectrometry Ë Refractive index for the sodium D line at ACS Chemicals meeting the specifications outlined 20 °C (or temperature indicated) by the American Chemical Society nm Nanometer APS Average particle size New product anhy Anhydrous NMR Nuclear magnetic resonance Å Angstrom OD Outer diameter ÷ Approximately optical gr. Suitable for optical applications approx. Approximately pc(s) Piece(s) Atm Atmospheres pH Value taken to represent the acidity or b.p. Boiling point in °C at 760mm pressure, unless alkalinity of an aqueous solution otherwise specified POR Price on request (c) Contained weight of active material ppb Parts per billion °C Celsius ppm Parts per million cc Cubic centimeter prec. Precipitated cm Centimeter Primary Analytical reagent of exceptional purity, cont. Contained Standard for standardizing volumetric solutions and cP Centipoise preparing reference standards cS Centistoke PTFE Poly(tetrafluoroethylene) d. Density Purified A grade of higher quality than technical, dec. Decomposes often used where there are no official dia. Diameter standards ea. Each P.T. Passes test eV Electron volt P.V. Pore volume °F Fahrenheit Reagent Reagent grade f.p. Flash point REM Rare earth metal FSSS Fisher sub-sieve sizer (REO) Rare earth oxide base - content of specific F.W. Formula weight rare earth element in comparison to total g Gram rare earths present g/l Grams per liter (gas density) S.A. Surface area GLC Suitable for use in gas liquid Sp.Gr. Specific gravity chromotography Sp.Rot. Specific rotation GC Gas chromotography subl. Sublimes HPLC High-performance liquid chromotography Tc Critical temperature ICP Inductively Coupled Plasma TLC Thin-layer chromotography ID Inner diameter TSCA Toxic Substance Control Act in Inch UN Hazardous material transportation incl Includes identification number IR Infrared œ Wavelength in nanometers J/mol.K Joule(s) per mole Kelvin wt Weight kg Kilogram w/w Weight/weight L or l Liter w/v Weight/volume lb Pound XRD X-ray diffraction m Meter È Air sensitive M Molarity of solution É Moisture sensitive mg Milligram Ê Hygroscopic æ Micro ß Light sensitive æg Microgram > Greater than meq Milliequivalent ² Greater than or equal to Merck The Merck Index < Less than æm Micrometer (micron) ³ Less than or equal to max Maximum [ ] Numbers in brackets after the chemical micron Micrometer description indicate the Chemical Abstract mm Millimeter Service Registry Number m.p. Melting point - mesh # 90% particles pass through screen having mol Mole a given mesh size mmol Millimole + mesh # 90% particles are retained by a screen M.W. Molecular weight having a given mesh size Mw Weighted averaged molecular weight Ì Denotes substance is listed in Toxic Mn Number averaged molecular weight Substance Control Act (TSCA) inventory Mw/Mn Monodispersity value 1 IA 18 VIIIA 1.00794 1 4.002602 2 Visit Our Website at H1 He2 1s 1s bp: -252.87°C bp: -268.9°C d: 0.089 g/ l www.alfa.com d: 0.179 g/l Hydrogen Helium 2 IIA 13 IIIA 14 IVA 15 VA 16 VIA 17 VIIA 6.941 3 9.012182 4 10.811 5 12.0107 6 14.0067
Load more

Recommended publications
  • Aldrich FT-IR Collection Edition I Library
    Aldrich FT-IR Collection Edition I Library Library Listing – 10,505 spectra This library is the original FT-IR spectral collection from Aldrich. It includes a wide variety of pure chemical compounds found in the Aldrich Handbook of Fine Chemicals. The Aldrich Collection of FT-IR Spectra Edition I library contains spectra of 10,505 pure compounds and is a subset of the Aldrich Collection of FT-IR Spectra Edition II library. All spectra were acquired by Sigma-Aldrich Co. and were processed by Thermo Fisher Scientific. Eight smaller Aldrich Material Specific Sub-Libraries are also available. Aldrich FT-IR Collection Edition I Index Compound Name Index Compound Name 3515 ((1R)-(ENDO,ANTI))-(+)-3- 928 (+)-LIMONENE OXIDE, 97%, BROMOCAMPHOR-8- SULFONIC MIXTURE OF CIS AND TRANS ACID, AMMONIUM SALT 209 (+)-LONGIFOLENE, 98+% 1708 ((1R)-ENDO)-(+)-3- 2283 (+)-MURAMIC ACID HYDRATE, BROMOCAMPHOR, 98% 98% 3516 ((1S)-(ENDO,ANTI))-(-)-3- 2966 (+)-N,N'- BROMOCAMPHOR-8- SULFONIC DIALLYLTARTARDIAMIDE, 99+% ACID, AMMONIUM SALT 2976 (+)-N-ACETYLMURAMIC ACID, 644 ((1S)-ENDO)-(-)-BORNEOL, 99% 97% 9587 (+)-11ALPHA-HYDROXY-17ALPHA- 965 (+)-NOE-LACTOL DIMER, 99+% METHYLTESTOSTERONE 5127 (+)-P-BROMOTETRAMISOLE 9590 (+)-11ALPHA- OXALATE, 99% HYDROXYPROGESTERONE, 95% 661 (+)-P-MENTH-1-EN-9-OL, 97%, 9588 (+)-17-METHYLTESTOSTERONE, MIXTURE OF ISOMERS 99% 730 (+)-PERSEITOL 8681 (+)-2'-DEOXYURIDINE, 99+% 7913 (+)-PILOCARPINE 7591 (+)-2,3-O-ISOPROPYLIDENE-2,3- HYDROCHLORIDE, 99% DIHYDROXY- 1,4- 5844 (+)-RUTIN HYDRATE, 95% BIS(DIPHENYLPHOSPHINO)BUT 9571 (+)-STIGMASTANOL
    [Show full text]
  • Design and Synthesis of FRET-Based Boronic Acid Receptors to Detect Carbohydrate Clustering and Development of Diacylglycerol-Ba
    University of Tennessee, Knoxville Trace: Tennessee Research and Creative Exchange Masters Theses Graduate School 12-2009 Design and Synthesis of FRET-Based Boronic Acid Receptors to Detect Carbohydrate Clustering and Development of Diacylglycerol-Based Lipid Probesto Investigate Lipid-Protein Binding Interactions Manpreet Kaur Cheema University of Tennessee - Knoxville Recommended Citation Cheema, Manpreet Kaur, "Design and Synthesis of FRET-Based Boronic Acid Receptors to Detect Carbohydrate Clustering and Development of Diacylglycerol-Based Lipid Probesto Investigate Lipid-Protein Binding Interactions. " Master's Thesis, University of Tennessee, 2009. https://trace.tennessee.edu/utk_gradthes/517 This Thesis is brought to you for free and open access by the Graduate School at Trace: Tennessee Research and Creative Exchange. It has been accepted for inclusion in Masters Theses by an authorized administrator of Trace: Tennessee Research and Creative Exchange. For more information, please contact trace@utk.edu. To the Graduate Council: I am submitting herewith a thesis written by Manpreet Kaur Cheema entitled "Design and Synthesis of FRET-Based Boronic Acid Receptors to Detect Carbohydrate Clustering and Development of Diacylglycerol-Based Lipid Probesto Investigate Lipid-Protein Binding Interactions." I have examined the final electronic copy of this thesis for form and content and recommend that it be accepted in partial fulfillment of the requirements for the degree of Master of Science, with a major in Chemistry. Michael Best, Major
    [Show full text]
  • A Calix[4]Arene Based Boronic Acid Catalyst for Amide Bond Formation: Proof of Principle Study
    The Free Internet Journal Paper for Organic Chemistry Archive for Arkivoc 2018, part v, 221-229 Organic Chemistry A calix[4]arene based boronic acid catalyst for amide bond formation: proof of principle study Asslly Tafara Mafaune and Gareth E. Arnott* Department of Chemistry and Polymer Science, Stellenbosch University, Private Bag X1, Matieland, South Africa Email: arnott@sun.ac.za Received 01-23-2018 Accepted 04-14-2018 Published on line 06-25-2018 Abstract A calix[4]arene boronic acid was synthesized and tested for catalysis in amide formation. The results were positive and paved the way for future designs, even though protodeboronation was observed under the conditions employed. Keywords: Amide bond catalysis, calix[4]arene boronic acid, protodeboronation DOI: https://doi.org/10.24820/ark.5550190.p010.492 Page 221 ©ARKAT USA, Inc Arkivoc 2018, v, 221-229 Mafaune, A. T. et al. Introduction The importance of amide bonds to human kind cannot be overemphasized; they are ubiquitous in nature and indispensable in chemical applications. They can be found in compounds such as the polymers that make our lives easier; the insecticides and agrochemicals that ensure that we have food on our tables; and most notably in the pharmaceutical drugs that help us live longer. Amide bonds are also part of the building blocks of biological systems, linking together amino acid units forming peptides, proteins and enzymes. The amide is arguably the most important functional group in chemistry and it also happens to be the most frequently synthesized in medicinal chemistry.1 Because of the versatility and importance of the amide bond, catalytic direct amide formation has been highlighted as a top priority reaction from a green chemistry viewpoint.
    [Show full text]
  • Phenyl Replacement Reactions: Solvent Effects on Reactions of Boroxines with Primary Amines
    Phenyl Replacement Reactions: Solvent Effects on Reactions of Boroxines with Primary Amines A thesis presented to the faculty of the Graduate School of Western Carolina University in partial fulfillment of the requirements for the degree of Master of Science in Chemistry. By Nicholas John Wilcox Director: Dr. William R. Kwochka Associate Professor of Chemistry Chemistry Department Committee Members: Dr. Channa De Silva, Chemistry Dr. Brian Dinkelmeyer, Chemistry March 2015 TABLE OF CONTENTS Page List of Figures ......................................................................................................................... iii List of Schemes ...................................................................................................................... vi Abstract................................................................................................................................... vii Chapter One: Introduction ....................................................................................................... 1 1.1 Background ...................................................................................................... 1 1.2 Complexes created by dative bonds ................................................................ 3 Chapter Two: Results and Discussion ..................................................................................... 7 2.1 Displacement and Complexation Reactions ..................................................... 7 Chapter Three: Conclusion ....................................................................................................
    [Show full text]
  • Frontiers in Iridium-Catalyzed CH Borylation
    Frontiers in Iridium-Catalyzed C-H Borylation: Attaining Novel Reactivity and Selectivity By Matthew Alan Larsen A dissertation submitted in partial satisfaction of the requirements for the degree of Doctor of Philosophy in Chemistry in the Graduate Division of the University of California, Berkeley Committee in charge: Professor John F. Hartwig, Chair Professor Robert G. Bergman Professor Alexis T. Bell Fall 2016 Abstract Frontiers in Iridium-Catalyzed C-H Borylation: Attaining Novel Reactivity and Selectivity By Matthew Alan Larsen Doctor of Philosophy in Chemistry University of California, Berkeley Professor John F. Hartwig, Chair The following dissertation discusses the development of novel methodology for the catalytic borylation of C-H bonds and includes in-depth studies on the mechanism and selectivity of these synthetic transformations. These methods include the borylation of heteroaryl C-H bonds, the selective borylation of benzylic C-H bonds, and the directed and undirected borylation of unactivated alkyl C-H bonds. Chapter 1 contains a comprehensive review of C-H borylation methodology. This review focuses on the initial development of catalytic C-H borylation and on the state-of- the-art of methodology for the undirected and directed borylation of aryl, benzylic, and alkyl C-H bonds. Additionally, this review highlights knowledge gaps and unsolved challenges. Furthermore, this review provides the author’s opinion on future directions for research on the borylation of C-H bonds. Chapter 2 describes the study of the iridium-catalyzed borylation of heteroaryl C- H bonds. Contained is an examination of the scope of the borylation of heterocycles containing more than one heteroatom and rules for predicting the site-selectivity of this reaction.
    [Show full text]
  • 1 Structure, Properties, and Preparation of Boronic Acid Derivatives Overview of Their Reactions and Applications Dennis G
    j1 1 Structure, Properties, and Preparation of Boronic Acid Derivatives Overview of Their Reactions and Applications Dennis G. Hall 1.1 Introduction and Historical Background Structurally, boronic acids are trivalent boron-containing organic compounds that possess one carbon-based substituent (i.e., a CÀB bond) and two hydroxyl groups to fill the remaining valences on the boron atom (Figure 1.1). With only six valence electrons and a consequent deficiency of two electrons, the sp2-hybridized boron atom possesses a vacant p-orbital. This low-energy orbital is orthogonal to the three substituents, which are oriented in a trigonal planar geometry. Unlike carbox- ylic acids, their carbon analogues, boronic acids, are not found in nature. These abiotic compounds are derived synthetically from primary sources of boron such as boric acid, which is made by the acidification of borax with carbon dioxide. Borate esters, one of the key precursors of boronic acid derivatives, are made by simple dehydration of boric acid with alcohols. The first preparation and isolation of a boronic acid was reported by Frankland in 1860 [1]. By treating diethylzinc with triethylborate, the highly air-sensitive triethylborane was obtained, and its slow oxidation in ambient air eventually provided ethylboronic acid. Boronic acids are the products of a twofold oxidation of boranes. Their stability to atmospheric oxidation is considerably superior to that of borinic acids, which result from the first oxidation of boranes. The product of a third oxidation of boranes, boric acid, is a very stable and relatively benign compound to humans (Section 1.2.2.3). Their unique properties and reactivity as mild organic Lewis acids, coupled with their stability and ease of handling, are what make boronic acids a particularly attractive class of synthetic intermediates.
    [Show full text]
  • Synthesis and Improvement of Self-Healing Boronate Ester Hydrogels
    SYNTHESIS AND IMPROVEMENT OF SELF-HEALING BORONATE ESTER HYDROGELS By CHRISTOPHER CHI-LONG DENG A DISSERTATION PRESENTED TO THE GRADUATE SCHOOL OF THE UNIVERSITY OF FLORIDA IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY UNIVERSITY OF FLORIDA 2017 © 2017 Christopher Chi-long Deng To friends and family and loved ones departed ACKNOWLEDGMENTS Numerous people have supported me to this point. I would like to thank all of my previous teachers throughout my education for the foundation they gave to me and the valuable work that they do for all students. I thank Dr. Yi Zhang for allowing me to work in her lab and gain valuable experience. I would also like to thank Dr. Bill Dolbier for sharing his passion for organic chemistry and assisting me in entering graduate school. Of course, I am grateful towards Dr. Brent Sumerlin for accepting me in his group. His expectations and guidance have been valuable in my scientific growth. Also, I would like to thank my committee of Dr. Ken Wagener, Dr. Stephen Miller, Dr. Adam Veige, and Dr. Anthony Brennan. I appreciate the time taken from their busy schedules and their advice over the years. I would also like to acknowledge the University of Florida, the Department of Chemistry, and the Butler Polymer Laboratory for the opportunity to pursue my doctorate and providing a supportive environment for myself and all graduate students. I am grateful to the members of the Sumerlin group. I have the most interaction with them on a daily basis, and it has been a tremendous source of support both personally and professionally.
    [Show full text]
  • RSC Advances PAPER
    View Article Online / Journal Homepage / Table of Contents for this issue RSC Advances Dynamic Article Links Cite this: RSC Advances, 2012, 2, 3968–3977 www.rsc.org/advances PAPER Palladium nanoshells coated with self-assembled monolayers and their catalytic properties Jun-Hyun Kim,*a Joon-Seo Park,b Hae-Won Chung,c Brett W. Bootea and T. Randall Lee*c Received 13th October 2011, Accepted 6th February 2012 DOI: 10.1039/c2ra00883a This report describes the preparation and characterization of palladium nanoshells protected with alkanethiol self-assembled monolayers (SAMs) and their application as efficient catalysts. Monodispersed silica core particles (y100 nm in diameter) were prepared and coated with a thin layer of palladium (y20 nm in thickness). Subsequently, the palladium nanoshells were treated with two separate alkanethiol adsorbates having different alkyl chain lengths: dodecanethiol (C12SH) and hexadecanethiol (C16SH). The optical properties, morphology, and chemical structure/composition of these nanoshells were thoroughly examined by ultraviolet-visible spectroscopy, field-emission scanning electron microscopy, transmission electron microscopy, energy-dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy, and Fourier-transform infrared spectroscopy. Additional studies revealed that these SAM-coated palladium nanoshells possessed enhanced colloidal stability in nonpolar solvents and in the solid state. Further, palladium nanoshells modified with C16SH SAM coatings were employed in the Suzuki coupling of phenylboronic acid with iodobenzene in organic solvents. Notably, these SAM-coated nanoshells afforded a greater conversion yield than that of related bare palladium nanoshells. Downloaded on 19 February 2013 Introduction palladium nanoparticles as catalysts depend largely on their size, shape, surrounding medium, and dispersion ability in organic The controlled fabrication of nanoscale metallic particles offers the solvents, which facilitates their manipulation and incorporation 1–5 opportunity to develop novel catalysts.
    [Show full text]
  • Boranes: Physical & Chemical Properties, Encyclopaedia of Occupational Health and Safety, Jeanne Mager Stellman, Editor-In
    Boranes: Physical & chemical properties, Encyclopaedia of Occupational Health and Safety, Jeanne Mager Stellman, Editor-in-Chief. International Labor Organization, Geneva. 2011. Chemical Name Colour/Form Boiling Point Melting Molecular Solubility in Relative Density Relative Vapour Inflam. Flash Auto CAS-Number (°C) Point (°C) Weight Water (water=1) Vapour Pressure/ Limits Point (°C) Ignition Density (Kpa) Point (°C) (air=1) BORON polymorphic: alpha- 2550 2300 10.81 insol Amorphous, 1.56x 580 3 -5 7440-42-8 rhombohedral form, clear 2.3 g/cm ; 10 red crystals; beta- alpha-- @ 2140 °C rhombohedral form, black; rhombohedral, - alpha-tetragonal form, 2.46 g/cm3; - black, opaque crystals with alpha-- metallic luster; amorphous tetragonal, - form, black or dark brown 2.31 g/cm3; - powder; other crystal beta-rhom- forms known bohedral, - 2.35 g/cm3 BORIC ACID, DISODIUM powder or glass-like 1575 741 201.3 2.56 g/100 g 2.367 SALT plates; white, free-flowing 1330-43-4 crystals; light grey solid BORON OXIDE rhombic crystals; 1860 450 69.6 2.77 g/100 g 1.8 1303-86-2 colourless, (amorphous); semitransparent lumps or 2.46 hard, white crystals (crystalline) BORON TRIBROMIDE colourless liquid 90 -46.0 250.57 reacts 2.6431 8.6 5.3 10294-33-4 @ 18.4 °C/4 °C @ 14 °C BORON TRICHLORIDE 12.5 -107 117.16 1.35 4.03 2.99 Pa 10294-34-5 @ 12 °C/4 @ 12.4 °C BORON TRIFLUORIDE colourless gas -99.9 -126.8 67.82 reacts 3.08g/1.57 l 2.4 10 mm Hg 7637-07-2 @ 4 °C @ -141 °C.
    [Show full text]
  • Pinacol Rearrangement
    Pinacol rearrangement The pinacol–pinacolone rearrangement is a method for converting a 1,2-diol to a carbonyl compound in organic chemistry. The 1,2-rearrangement takes place under acidic conditions. The name of the rearrangement reaction comes from the rearrangement of pinacol to pinacolone.[1] This reaction was first described by Wilhelm Rudolph Fittig in 1860 of the famed Fittig reaction involving coupling of 2 aryl halides in presence of sodium metal in dry ethereal solution.[2] Contents Mechanism Example of asymmetrical pinacol rearrangement Stereochemistry of the rearrangement History See also References Mechanism In the course of this organic reaction, protonation of one of the –OH groups occurs and a carbocation is formed. If the – OH groups are not alike (i.e. the pinacol is asymmetrical), then the one which creates a more stable carbocation participates in the reaction. Subsequently, an alkyl group from the adjacent carbon migrates to the carbocation center. The driving force for this rearrangement step is believed to be the relative stability of the resultant oxonium ion. Although the initial carbocation is already tertiary, the oxygen can stabilize the positive charge much more favorably due to the complete octet configuration at all centers. It can also be seen as the -OH's lone pairs pushing an alkyl group off as seen in the asymmetrical pinacol example. The migration of alkyl groups in this reaction occurs in accordance with their usual migratory aptitude, i.e.hydride > phenyl carbanion > tertiary carbanion (if formed by migration) > secondary carbanion (if formed by migration) > methyl carbanion. {Why carbanion? Because every migratory group leaves by taking electron pair with it.} The conclusion is that the group which stabilizes the carbocation more effectively is migrated.
    [Show full text]
  • Microwave Assisted Petasis Boronic-Mannich Reactions Neville J
    Tetrahedron Letters Tetrahedron Letters 45 (2004) 993–995 Microwave assisted Petasis boronic-Mannich reactions Neville J. McLean, Heather Tye* and Mark Whittaker Evotec OAI, 151 Milton Park, Abingdon, Oxfordshire OX14 4SD, UK Received 15 September 2003; revised 10 November 2003; accepted 21 November 2003 Abstract—We have used a design of experiments (DOE) approach to optimise rapidly a set of microwave assisted conditions for the Petasis reaction. The optimal conditions involved the microwave heating of the reaction components in dichloromethane (1 M concentration) at 120 °C for 10 min in a focussed microwave (CEM Explorer). These conditions were successfully applied to a range of Petasis reactions employing either glyoxylic acid or salicylaldehyde as the carbonyl component along with a number of aryl/ heteroaryl boronic acids and amine components. Ó 2003 Elsevier Ltd. All rights reserved. 1. Introduction performing best and hindered primary amines per- forming well in some cases. Anilines and hydrazines The Petasis or boronic-Mannich reaction involves the have also been applied to the Petasis reaction to good reaction between an aldehyde, an amine and a boronic effect.9 acid (Scheme 1). The reaction is most frequently carried out with an aldehyde possessing a coordinating group, In general the reaction conditions employed for the which can form a boronate complex and thus facilitate Petasis reaction involve stirring at room temperature for the carbon–carbon bond forming step. The two alde- periods of 24 h or more. The solvents employed vary hydes most commonly used are glyoxylic acid 1 and depending on the application and include dichlorome- salicylaldehyde 2 although other hydroxy aldehydes thane (DCM), toluene, ethanol and acetonitrile.
    [Show full text]
  • Short Synthesis of Skeletally and Stereochemically Diverse Small Molecules by Coupling Petasis Condensation Reactions to Cyclization Reactions**
    Angewandte Chemie Multicomponent Reactions DOI: 10.1002/anie.200600497 Short Synthesis of Skeletally and Stereochemically Diverse Small Molecules by Coupling Petasis Condensation Reactions to Cyclization Reactions** Naoya Kumagai, Giovanni Muncipinto, and Stuart L. Schreiber* Herein, we report a short and efficient synthetic pathway that uses intramolecular cyclization reactions of readily synthe- sized and densely functionalized amino alcohols. The research illustrates the implementation of a strategy that enables the synthesis, in only three to five steps, of a diverse collection of single-isomer small molecules whose members have over 15 different types of skeleton. In the future, this research should also enable the consequences of the unique structural features of the compounds in small-molecule screens to be deter- mined.[1,2] We used the Petasis three-component, boronic acid Mannich reaction[3] followed by an amine propargylation to yield b-amino alcohols 1. These compounds bear polar (amino, hydroxy, ester) and nonpolar (alkene, alkyne, cyclo- propane) functionalities strategically placed as handles for subsequent skeletal diversification reactions (Scheme 1). The Petasis reaction of (S)-lactol 2a (from l-phenyllactic acid), l-phenylalanine methyl ester (3a), and (E)-2-cyclo- propylvinylboronic acid (4) proceeded smoothly under ambi- ent conditions in EtOH to afford the anti diastereomer 5aa exclusively in 85% yield.[4] The same conditions but with (R)- lactol 2b afforded the corresponding (2R,3S) isomer 5ba exclusively (Scheme 2). These reactions indicate that the secondary hydroxy group adjacent to the intermediate imines directs the stereochemical outcome of the reaction, over- riding any directing effects of the stereocenter in 3a.[3b] These [*] Prof.
    [Show full text]