Catalytic Asymmetric Vinylation

The synthetic utility of the vinylic sulfide and selenide approach is exemplified by the synthesis of enantio-pure (i )-(-)-ipsdienol, an insect aggregation pheromone (Sch. 13) [54], Kabat and Uskokovic have demonstrated the asymmetric catalytic synthesis of la,25-dihydroxyvitamin D3 (la,25(OH)2D3) A-ring synthon by means of a glyoxylate-ene reaction catalyzed by BINOL-Ti complex (1) (Sch. 14) [55]. 

BINOL-Ti catalysis can also be used for the carbonyl-ene reaction with formaldehyde or vinyl and alkynyl analogs of glyoxylates in an asymmetric catalytic desymme-trization (vide infra) approach to the asymmetric synthesis of isocarbacycline analogs (Sch. 16) [61]. 

Barrett and Kamimura have developed a stepwise asymmetric catalytic variant of the Baylis-Hillman reaction. A stoichiometric amoimt of nucleophile, MesSi-SPh or MesSi-SePh (7.174) is added, but only a catalytic amount of Lewis acid (7.175) in the reaction between methyl vinyl ketone (7.168) and acetaldehyde (7.176). The aldol adduct (7.177) was subjected to oxidation and selenoxide elimination to give the product (7.178), which is the same as the product from a Baylis-Hillman reaction. 

Walsh developed an efficient protocol for the asymmetric catalytic vinylation of a variety of aldehydes and ketones, using the vinylzinc species generated in situ by treatment of terminal alkynes with Schwartz s reagent for hydrozirconation, followed by transmetallation to zinc via reaction with Me2Zn. Under the catalysis of titanium complex of the chiral dihydroxyl bis (sulfonamide) ligand, the reaction provides access to the corresponding secondary or tertiary allylic alcohols in high yields and excellent enantiomeric excesses [65] (Scheme 14.13). 

Dieguez M, Pamies O, Ruiz A, Castillon S, Claver C. Chiral diphosphites derived from D-glucose new ligands for the asymmetric catalytic hydroformylation of vinyl arenes. Chem. Eur. J. 2001 7 3086-3094. 

In an extension of this work, the Shibasaki group developed the novel transformation 48—>51 shown in Scheme 10.25c To rationalize this interesting structural change, it was proposed that oxidative addition of the vinyl triflate moiety in 48 to an asymmetric palladium ) catalyst generated under the indicated conditions affords the 16-electron Pd+ complex 49. Since the weakly bound triflate ligand can easily dissociate from the metal center, a silver salt is not needed. Insertion of the coordinated alkene into the vinyl C-Pd bond then affords a transitory 7t-allylpalladium complex 50 which is captured in a regio- and stereocontrolled fashion by acetate ion to give the optically active bicyclic diene 51 in 80% ee (89% yield). This catalytic asymmetric synthesis by a Heck cyclization/ anion capture process is the first of its kind. 

Aryl, Vinyl, and Alkyl Aziridines Catalytic Asymmetric Ylide-mediated Aziridination... 

The catalytic enantioselective addition of vinylmetals to activated alkenes is a potentially versatile but undeveloped class of transformations. Compared to processes with arylmetals and, particularly alkylmetals, processes with the corresponding vinylic reagents are of higher synthetic utility but remain scarce, and the relatively few reported examples are Rh-catalysed conjugate additions. In this context, Hoveyda et al. reported very recently an efficient method for catalytic asymmetric allylic alkylations with vinylaluminum reagents that were prepared and used in Thus, stereoselective reactions... 

The Heck reaction has proven to be an extremely useful method for the formation of C-C bond at a vinyl carbon centre. There are numerous reported examples of enantioselctive Pd catalyzed C-C bond forming reactions.10"13 Surprisingly, reports of Heck transformations using amino acid based phosphine, phosphinite ligands are rare. Recently Gilbertson reported a proline derived phosphine-oxozoline ligand in a catalytic asymmetric Heck reaction.5 In this paper we present some novel amino acids derived ligands as part of a catalytic system for use in asymmetric Heck reactions. 

Catalytic enantioselective nucleophilic addition of nitroalkanes to electron-deficient alke-nes is a challenging area in organic synthesis. The use of cinchona alkaloids as chiral catalysts has been studied for many years. Asymmetric induction in the Michael addition of nitroalkanes to enones has been carried out with various chiral bases. Wynberg and coworkers have used various alkaloids and their derivatives, but the enantiomeric excess (ee) is generally low (up to 20%).199 The Michael addition of methyl vinyl ketone to 2-nitrocycloalkanes catalyzed by the cinchona alkaloid cinchonine affords adducts in high yields in up to 60% ee (Eq. 4.137).200... 

The catalytic asymmetric aminohydroxylation of a variety of styrene derivatives, vinyl aromatics, and some other olefins using osmium tetroxide... 

Various catalytic or stoichiometric asymmetric syntheses and resolutions offer excellent approaches to the chiral co-side chain. Among these methods, kinetic resolution by Sharpless epoxidation,14 amino alcohol-catalyzed organozinc alkylation of a vinylic aldehyde,15 lithium acetylide addition to an alkanal,16 reduction of the corresponding prochiral ketones,17 and BINAL-H reduction18 are all worth mentioning. 

Abstract This chapter presents the latest achievements reported in the asymmetric hydroformylation of olefins. It focuses on rhodium systems containing diphosphites and phosphine-phosphite ligands, because of their significance in the subject. Particular attention is paid to the mechanistic aspects and the characterization of intermediates in the hydroformylation of vinyl arenes because these are the most important breakthroughs in the area. The chapter also presents the application of this catalytic reaction to vinyl acetate, dihydrofurans and unsaturated nitriles because of its industrial relevance. 

Catalytic asymmetric methylation of 6,7-dichloro-5-methoxy-2-phenyl-l-indanone with methyl chloride in 50% sodium hydroxide/toluene using M-(p-trifluoro-methylbenzyDcinchoninium bromide as chiral phase transfer catalyst produces (S)-(+)-6,7-dichloro-5-methoxy-2-methyl-2--phenyl-l-indanone in 94% ee and 95% yield. Under similar conditions, via an asymmetric modification of the Robinson annulation enqploying 1,3-dichloro-2-butene (Wichterle reagent) as a methyl vinyl ketone surrogate, 6,7 dichloro-5-methoxy 2-propyl-l-indanone is alkylated to (S)-(+)-6,7-dichloro-2-(3-chloro-2-butenyl)-2,3 dihydroxy-5-methoxy-2-propyl-l-inden-l-one in 92% ee and 99% yield. Kinetic and mechanistic studies provide evidence for an intermediate dimeric catalyst species and subsequent formation of a tight ion pair between catalyst and substrate. 

Satoh T, Miura M (2007) Catalytic Arylation and Vinylation Reactions Directed by Anionic Oxygen Functions via Cleavage of C - H and C - C Bonds. 24 61-84 Savoia D (2005) Progress in the Asymmetric Synthesis of 1,2-Diamines from Azomethine Compounds. 15 1-58... 

A catalytic amount of ketone 26 was used to investigate the substrate scope of the asymmetric epoxidation. High enantioselectivities can be obtained for a wide variety of trans- and trisubstituted olefins (Table 3, entries 1 ) [54]. Simple trans-olefins, such as franx-7-tetradecene, can be epoxidized in high yield and enantiomeric excess, indicating that this asymmetric epoxidation is generally suitable for frani-olefms. 2,2-Disubstituted vinyl silanes are epoxidized in high ees (Table 3, entries 5, 6) and enantiomerically enriched 1,1-disubstituted epoxides can be... 

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