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Asymmetric Hydroxylation of Enolates with Nsuifonyloxaziridines

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Chsm. Rev. 1992, 92, 919-934 919 Asymmetric Hydroxylation of Enolates with NSuifonyloxaziridines Franklin A. Davis' and BangChi Chen oepam01 "fsby. mx.91 m-, mnadelphlb. ~,WYAJ.WI~ 19104 Recsfvd November 8. 199 1 (Flevked Msnusuipt Recsfvd Fsbruary 8. 1992 ) Contents I. Introduction 919 'r 11. Reagents 920 4 f Ill. Mechanism of Oxygen Transfer 921 IV. Transition-State Models 921 V. Asymmetric Hydroxylation of Enolates 922 A. Substrate-Induced Hydroxylations 922 1. Ketones 922 2. Esters 922 ,*"' 3. Lactones 923 :L E. Auxlllary-Induced Hydroxylations 923 1. Ketones 923 2. Aldehydes 923 3. Esters 924 Franklin A. Davis was born in Des Moines. Iowa. He recelved his 4. AmMes 924 B.S. degree in 1962 from the University of WiScOnsln and was granted e Ph.D. degree in 1966 from Syracuse University working 5. CarboximMes 924 under Donald C. Dimer. After two years with Michael J. S. Dewar C. Reagent-Induced Hydroxylations 925 as a Welch PoSMoctoral Fellow at the University of Texas he joined 1. Ketones 925 the facuity at Drexel University in 1968 where he is currently the George S. Sasin Professor of Organic Chemistry. In 1980 he 2. Esters 926 received Drexel University's Research Achievement Award and in 3. Amides 927 1982 the PhiladelDhia ACS Section Award. Dr. Davis' research Interests lie in the area of asymmetric synthesis. molecular 4. Lactones 927 recognMon.and new syntheticmethodspartkularlyrelatedtoenalF 5. Enones 927 tioselective oxidations. me development of new methods for the D. Double Stereodifferentlation 927 regio- and stereoselective fluorination of organic molecules is a recent focus VI. Synthesis of Natural Products 928 A. DlastereOSelectke Hydroxylations 928 1. Ketones 928 2. a.8-Unsaturated Esters 929 3. Lactones 930 4. Lactams 930 5. Carboxlmldes 930 8. fl-Dicarbonyls 931 E. Enantioselectke Hydroxylations 931 1. Ketones 931 2. &Keto Esters 931 VII. Summary 932 VIII. Acknowledgments 932 IX. References 933 BangChl Chen was born in the remote countryslde of Zhejlang Province, PRC in 1964. He received his BSc. degree In chemlsby I. Introductlon In 1984 from Hangzhou University where he was an Instructw. The availability of efficient methods for the con- teaching undergraduate organic chemistry foliowlng graduatkm. During thh time period he conducted research wim Xlan Huang. enantiopure carbonyl struction of a-hydroxy com- In 1987 he began graduate study at Drexel University and. in the pounds [RR'C(OH)C(O)Zl is of considerable current following year, thesis research under the guidance of Frankiln A. interestbecause thisstructuralarray is featuredinmany Davis, Heobtainedthe M.Sc.degreein 1989andthePh.D.in 1991 biologically relevant molecules. Compounds containing and, In #a same year, joined the BrlstoCMeyers Squibb Company In Syracuse New York. He has aUthored and/or co-authored 28 this moiety are also useful auxiliaries' and synthons2 research and review articles. for the asymmetric synthesis of natural products including antitumor agents, antibiotics, pheromones, to the stereogenic carbon because biological activity is and sugars. Of particular concern in these structures often critically dependent upon ita orientation. The is the stereochemistry of the hydroxy group attached significance of the a-hydroxy carbonyl unit in bioac- 0009-2665~92/07926919$10.00~0 0 1992 Amwlcan Chemical Society 920 Chemical Reviews, 1992, Vol. 92, No. 5 Davls and Chen Scheme I. Strategies for the Preparation of versatile method for the preparation of this structural a-Hydroxy Carbonyl Compounds array. Furthermore both enantiomeric forms of a-hy- droxy carbonyl compounds are available by use of the RkR' vmol' RqR' (1) antipodal oxidizing reagents. By using aprotic oxidants 0 0 such as dioxygen,13 dibenzyl pero~ydicarbonate,'~ MoOPH,l5J6 or MoOPD17 to effect the oxidation product, diastereoselectivity is induced by stereodi- Rd\rlR' IR"l+_ RTR' (2) recting groups or chiral auxiliaries in the enolate. 0 0 In 1984, Davis and co-workers18 introduced racemic trans-(A) -2- (phenylsulfonyl)-3-phenyloxaziridine(la) l9 for the direct hydroxylation of enolates. The avail- ability of enantiopure N-sulfonyloxaziridines such as ldY2O 2c,212d,21 and 322-26for the asymmetric hy- droxylation of enolates makes possible control of ste- reoselectivity by the reagent. This article is intended to summarize progress in the asymmetric hydroxyla- tion of enolates using N-sulfonyloxaziridines, with particular emphasis on their applications in natural Scheme 11. Asymmetric Oxidation of Enolates with product synthesis. Both diastereoselective and enan- N-Sulfonyloxaziridines tioselectivehydroxylations of enolates by these reagents will be covered. Some aspects of this topic have been reviewed el~ewhere.~'-~~ 0 I 6) q, Y so* 0 R $6 PI A 2 3 tive compounds and its remarkable versatility as a chi- ral synthon and auxiliary has stimulated the develop- R R Ar 01 R ment of many methods for its synthesis. These methods la Ph Ph 2a 3a H H differ mainly in the substrates used (i.e. the oxidation lb p-MePh Ph 2b Ph 3b CI H state of the carbon atom adjacent to the carbonyl group) IC p-MePh o-MePh 3c McO H and can be categorized as nonoxidative (eqs 1-3) and 3d H Bn 2c + oxidative (eq 4) procedures (Scheme I). 3e H p-MeOBn The classical method for the preparation of optically 3f H p-CF3Bn active a-hydroxy carbonyl compounds involves a sub- stitution reaction using optically active a-amino acids (L = NH2)3and a-halo amides (L = C1, Br)4as starting le Of$ 2-CI-5-@NPh materials (eq 1). Homologation is another approach in which chiral auxiliaries and stereodirecting groups, incorporated into the substrate, are used to induce di- 11. Reagents astereoselectivity (eq 2).5 Addition of hydride or a car- banion to a-dicarbonyl compounds (or their monoketal N-Sulfonyloxaziridines are prepared by the biphasic derivatives) has also been used to prepare chiral a- basic oxidation of the corresponding sulfonimine with hydroxy carbonyl compounds (eq 3). Either chiral n-CPBA or 0x0ne.l~ Oxidation of acyclic chiral sul- reducing reagents! chiral reducing catalysts? chiral or- fonimines affords mixtures of oxaziridine diastereoi- ganometallic reagents,8or chiral auxiliariesghave been somers 1, requiring separation by crystallization (eq employed to induce stereoselectivity. Chiral additives 5).20 Similar results are observed on oxidation of the have also been used in some of these transformations.lO sulfonimines corresponding to 2 which limits their Generally these nonoxidative procedures are limited production on a large scale.21 In contrast the (cam- to the synthesis of acyclic derivatives. phorsulfony1)oxaziridinederivatives 3 [tetrahydro-9,9- Two oxidative methods have been developed for the dimethyl-4H-4a,7-methanooxazirino[3,2-i] [2,1] benz- synthesis of a-hydroxy carbonyl compounds. One, isothiazole 3,3-dioxidel are readily available on multi- known as the Rubottom reaction, requires the prefor- gram and kilogram scales because the endo face of the mation of a silyl enol ether from the carbonyl compound. C-N double bond in 4 is blocked, affording on oxidation The silyl enol ether is then oxidized with reagents such a single oxaziridine isomer (eq 6).22 (Camphorylsul- as m-chloroperbenzoicacid (m-CPBA)llor N-sulfonyl- fony1)oxaziridine(3a) and (8,8-dichlorocamphorsulfo- oxaziridines.12 The past several years have seen the ny1)oxaziridine (3b) [8,8-dichlorotetrahydro-9,9-dim- emergence of the second method, the direct oxidation ethyl-4H-4a,7-methanooxazirino[3,2-i][2,11 benziso- of enolates, as the most widely used method for the thiazole 3,3-dioxidel are commercially available from stereoselective synthesis of the a-hydroxy carbonyl Aldrich Chemical Co. and Fluka, respectively. array (Scheme 11). This protocol affords the target Sulfonimines relating to oxaziridines 1 and 2 are functionality directly and is effective for both acyclic prepared by condensing sulfonamides with aromatic and cyclic substrates. The great diversity of metal eno- aldehydeslg and by reacting lithium reagents with late types makes their oxidation potentially the most saccharin, respectively.21 The (-)-(camphorsulfony1)- Asymmetrlc Hydroxylation of Enolates Chemical Reviews, 1992, Vol. 92, No. 5 921 Scheme 111, Synthesis of the (Camphorsulfony1)- imine Derivatives m-CPBA RS&N=CHAr 4 3 a) X=Y=H, b) X=C1, Y=H, c) X=OMe. Y=H d) X=H, Y=p-2-Bn 4c I- 6 4d imine 4a is the common intermediate for the prepa- ration of the (camphorsulfony1)imine derivatives 4 Scheme IV. General Mechanism for Enolate (Scheme 111) and is prepared in 90 '7% overall yield from Oxidation with N-Sulfonyloxaziridine (1s)-(+)-10-camphorsulfonic acid.22 The (7,7-dichlo- 0 M+ rocamphorsulfony1)imine 4b arises via halogenation of azaenolate 5.23 Carbon electrophiles generally react with 5 at the azaenolate nitrogen atom to give enam- ines which are hydrolytically unstable.25 However, di- anion 6 undergoes smooth monoalkylation a to the sulfonyl moiety to give 1:l mixtures of exo- and endo- sulfonimines 4d.25326 With selenium dioxide 4a gives the (-)-(3-oxocamphorsulfonyl)imine 7 which is trans- formed to the (7,7-dimethoxycamphorsulfonyl)imine 4c in 70% overall yield.24 The antipodal reagents are .A("' available starting from (1R)-(-)-10-camphorsulfonic 0 acid. 10 I I I. Mechanism of Oxygen Transfer aziridines (Scheme IV).S8 The enolate anion attacks at the oxaziridine oxygen atom to give hemiaminal in- Theoretical3135and e~perimental~~studies have sug- termediate 8 which fragments to the sulfonimine 9 and gested an sN2type mechanism for the transfer
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    Green Chemistry View Article Online COMMUNICATION View Journal | View Issue Hydrogen peroxide/dimethyl carbonate: a green system for epoxidation of N-alkylimines and Cite this: Green Chem., 2016, 18, 4859 N-sulfonylimines. One-pot synthesis of N N Received 20th May 2016, -alkyloxaziridines from -alkylamines and Accepted 22nd July 2016 (hetero)aromatic aldehydes† DOI: 10.1039/c6gc01394e a,b b a www.rsc.org/greenchem Jamil Kraïem, Donia Ghedira and Thierry Ollevier* A green method for epoxidation of imines using an environ- and oxidation with buffered oxone.24 Perfluoro-oxaziridines mentally benign oxidant system, H2O2/dimethyl carbonate, was have also been prepared by the oxidation of the corresponding N 25 developed. -Alkyloxaziridines were prepared in high yields from perfluoro-imines with H2O2 in the presence of a base. These N 26 11,17 Creative Commons Attribution 3.0 Unported Licence. -alkylamines and (hetero)aromatic aldehydes in one-pot fashion, methods usually use toxic solvents such as CH3CN and 19b whereas N-sulfonyloxaziridines have been prepared by using the CH2Cl2. Furthermore, most of them generate stoichiometric same oxidant system and 5 mol% of Zn(OAc)2·2H2O as catalyst. amounts of undesirable waste, and require tedious work-up and purification. 1 Oxaziridines, first reported by Emmons in 1957, exhibit Recently, such synthetic routes utilizing hazardous solvents unusual and distinctive reactivity, which is linked to the and reagents and generating toxic waste have become discour- nature of their N-substituent. For example, N-sulfonyloxaziri- aged and there have been much efforts to develop safer and dines have been used as electrophilic oxygenating agents for environmentally-benign alternatives.
  • A Thesis Entitled "RING CLEAVAGE of OXAZIRID]NES" Submitted By

    A Thesis Entitled "RING CLEAVAGE of OXAZIRID]NES" Submitted By

    A thesis entitled "RING CLEAVAGE OF OXAZIRID]NES" submitted by ANA MARIA FELIX TRINDADE LOBO in partial fulfilment of the requirements for the Degree of Doctor of Philosophy in the Faculty of Science University of London Imperial College, October,1971 London, S.W.7. i 2 ABSTRACT A general survey of the chemistry of oxaziridines is presented, previous studies on the mechanism of the acid and base catalysed hydrolysis are critically reviewed and the results discussed in relation with the hydrolysis of compounds with related structures. Results of the acid hydrolysis of several oxaziridines are reported and agree with previous findings. These accord with a mechanism involving the breakdown of an 0-conjugate acid intermediate to give either a carbonium ion or an immonium ion structure, which subsequently reacts-with water. The importance of each pathway depends on the nature of the 3-substituent. The proton of to the ring nitrogen seems to be involved in the rate determining step for the reaction of 2-primary-alkyl 3-alkyl oxaziridines. For 2-secondary-alkyl 3- alkyl compounds extensive migration of an 45( group occurs and steric requirements and migratory aptitudes seem to be important. Inves- tigations of the site of protonation suggest N as the most likely site, although hydrolysis probably proceeds via the 0-conjugate acid: pK values for oxaziridines reflect the nature of the 3-substituent A as well as the degree of branching at position 2 and lie in the range -1.9 to +0.30. Results of basic hydrolysis of several oxaziridines are reported and are consistent with earlier findings.