CHARGE-DIRECTED CONJUGATE ADDITION-REACTIONS OF SILYLATED ALPHA-BETA-UNSATURATED AMIDATE ANIONS

A variety of N-substituted alpha-silylated-alpha,beta-unsaturated amid ate anions (2) have been found to be excellent Michael acceptors in ch arge-directed conjugate addition reactions with Grignard and organolit hium reagents. The effects of olefin substitution, Si-substitution, N- substitution, and amidate counterion have been studied. Anionic accept ors may be prepared in situ by the addition of silylated vinyllithium reagents to isocyanates and then allowed to undergo conjugate addition reactions with subsequently added nucleophiles, but it was found to b e more efficient to isolate neutral acceptors and regenerate the accep tor anion through the use of excess nucleophile. Beta-Substituted acce ptors were found to react only with reactive organolithium reagents wh ile a beta,beta-disubstituted acceptor failed to undergo conjugate add ition reactions. A primary amide acceptor (14d) also undergoes additio n reactions with larger quantitites of nucleophiles suggesting that di anionic amidate acceptors (31) are involved. Diene acceptor 24 was fou nd to undergo a 1,6-addition reaction with n-BuLi. Sodium and potassiu m amidate salts were found to be inferior to lithium and magnesium sal ts in addition reactions in keeping with the expectation that an incre ase in carbonyl-group charge burden retards conjugate reactions. Triph enylsilyl-containing acceptor 16 was found to be more reactive in reac tions with n-BuMgCl but less reactive with bulkier tert-BuMgCl. Adduct dianions can be monoalkylated with alkyl iodides and used in Peterson olefination reactions.