Charge-directed conjugate addition reactions of silylated α-β- unsaturated amidate anions

Article abstract of DOI:10.1021/jo00078a028

A variety of N-substituted α-silylated-α,β-unsaturated amidate anions (2) have been found to be excellent Michael acceptors in charge-directed conjugate addition reactions with Grignard and organolithium reagents. The effects of olefin substitution, Si-substitution, N-substitution, and amidate counterion have been studied. Anionic acceptors 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 be more efficient to isolate neutral acceptors and regenerate the acceptor anion through the use of excess nucleophile. β-Substituted acceptors were found to react only with reactive organolithium reagents while a β,β-disubstituted acceptor failed to undergo conjugate addition reactions. A primary amide acceptor (14d) also undergoes addition reactions with larger quantitites of nucleophiles suggesting that dianionic amidate acceptors (31) are involved. Diene acceptor 24 was found to undergo a 1,6-addition reaction with n-BuLi. Sodium and potassium amidate salts were found to be inferior to lithium and magnesium salts in addition reactions in keeping with the expectation that an increase in carbonyl-group charge burden retards conjugate reactions. Triphenylsilyl-containing acceptor 16 was found to be more reactive in reactions with n-BuMgCl but less reactive with bulkier tert-BuMgCl. Adduct dianions can be monoalkylated with alkyl iodides and used in Peterson olefination reactions.