Lactams chiral ylides

The reaction was further developed to form a wide range of p-lactam-based products (52). Treatment of the racemic ylide processor 186 with suitable sulfur-based thiocarboxylate or thiocarbonate dipolarophiles gave rise to the expected racemic penams 189 and 190 and penems as single regioisomers (Scheme 3.54). Once again, the use of the chiral dipolarophile 186 furnished the cycloaddition product 191 with complete enantiomeric integrity. Similarly, the use of aldehydes... 

Chiral bicyclic lactams have been successfully utilized by Meyers as chiral dipolarophiles in highly diastereoselective azomethine ylide cycloadditions (73). Treatment of the ylide precursor 218 with the unsaturated, non-racemic dipolar-ophile 219 in the presence of a catalytic amount of TFA led to the formation of tricyclic adducts 220 and 221 in excellent yields (85-100%). The diastereofacial preference for the reaction was dependent on the nature of R with a methyl group... 

Cinchona alkaloids possess a nucleophilic quinuclidine structure and can perform as versatile Lewis bases to react with ketenes generated in situ from acyl halides in the presence of an acid scavenger. The resulting ketene enolates can react with electrophilic C=0 or C=N bonds to deliver chiral [i-lactones [5] or [i-lactams [6], respectively, in a [2 + 2] cycloaddition manner, which is discussed in Chapter 5 in detail. Gaunt et al. also developed practical one pot cydopropanation processes mediated by the modified cinchona alkaloids via ammonium ylide intermediates [7]. Although the catalytic strategy has been well established, the utilization of ammonium enolate based [4 + 2] cycloaddition is rare probably because of the relative unreactivity of the... 

A more common strategy for stepwise asymmetric cyclopropanation is the use of chiral electrophiles. Meyers has used bicyclic lactams (c/. Scheme 3.19, 3.20) [145,146] as electrophilic auxiliaries in sulfur ylide cyclopropanations [147]. These auxiliaries, for reasons that are not entirely clear, are preferentially attacked from the a-face. After separation of the diastereomers, the amino alcohol auxiliary may be removed by refluxing in acidic methanol or reductively [145]. This methodology has been used in asymmetric syntheses of cw-deltamithrinic acid and dictyopterene C, illustrated in the inset of Scheme 6.40 [145]. 

In asymmetric ylide cyclopropanations with achiral ylides vinylsulfoxides/ bicyclic y-lactams as well as exo-cyclic methylene compounds were examined as chiral Michael acceptors. Bicyclic compounds proved to be most efficient. 

Besides the dipolarophiles discussed above, chiral unsaturated (R)s-p-tolyl vinylsulfoxides A have been studied, too. In addition, chiral unsaturated bicyclic lactams B have been applied successfully by Meyers et al. as dipolarophiles in cycloadditions with azomethine ylides. ... 

Chiral stabilized ylides were prepared by the reaction of the Bestmann ylide ((triphenylphosphoranylidene)ketene) with camphor-derived lactams that were used directly or after modification by alkylation in Wittig olefinations. Representative examples are shown in Scheme 92. The products can be regarded as chiral building blocks. ... 

The phosporic acid (261) catalysed three component reaction involving asymmetric 1,3-dipolar cycloaddition of electron-deficient azomethine ylides (327), aromatic aldehydes (328) and 2-aminomalonates (329) to provide to novel 2,5-dihydropyrrole derivatives (330) with potential bioactivities with enantioselectivities of up to >99% ee (Scheme 86). The Bronsted acids (253) catalysed intermolecular enantioselective alkylation of indoles (332) with cx,p-unsaturated y-lactams (331) thus providing a highly enantioselective method for the synthesis of chiral pyrroli-dinones (333) containing indole moieties, with enantioselectivity (up to 95% ee), has been described by Huang et al. (Scheme 87). " ... 

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