Silylimines, addition reactions

Attempts to extend the organometallic addition reaction to A -trialkylsilylimines derived from enoliz-able ketones have been frustrated by difficulties encountered in the preparation of these silylimines (due to competitive enolization), in addition to the existence of a tautomeric equilibrium between desired silylimines and the corresponding enamines. As a result, addition products (formed in low yield) are accompanied by significant amounts of starting materials (presumably generated via enamine hydrolysis).However, silylimines derived from enolizable aldehydes reportedly can be generated and trapped in situ with ester enolates to form 3-lactams (18-60% yield). 

Allmenginger reported the preparation of Phe- /[(F)-CF=CH]-Gly in racemic form via -selective HWE reaction, yielding a-fluoroenoate 7. Conversion of the (Zs)-aldehyde 8 to N-silylimine, followed by the addition of the Grignard reagent afforded amine 9 without isomerization of the double bond (see Scheme 10.2) [13]. 

The same group has recently reported new findings on the reaction of -BuLi with W-(metallo)imines [23b]. They examined the addition of -BuLi to an AT-alu-minoimine, W-borylimine, and AT-silylimine in the presence of chiral nitrogen ligands including (-)-sparteine and proline-derived amino alcohols (Scheme 5). 

Condensation reactions between the lithium dianion of (S)-ethyl 3-hydroxybutyrate (127 R = OH) and cinnamaldimine (128), in connection with the synthesis of thienamycin, have been reported independently by three groups Georg et Cainelli et a/. " and Hart and Ha. Their results are summarized in Scheme 27 and Table 17 (entries 1-3) analogous reactions of dianion (127) with A -silylimines are discussed in Section 4.1.3.3.1. Of the four possible diastereomeric 3-lactams (129)-(132) that can be produced in this reaction, the two that prevail, (129) and (130), contain the predicted relative stereochemistry at C-3 and C-T. Subsequent inversion of the hydroxy groups of (129) and (130) led to intermediates which constituted formal total syntheses of thienamycin. " " In addition to 3-lactams (129) and (130), trans 3-lactam (131) is sometimes isolated but cis 3-lactam (132) is never observed. The product distributions are not uniform and may reflect the different bases used or the rate at... 

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