REACTIONS OF TIN(IV) ENOLATES OBTAINED FROM O-STANNYL KETYLS UNDER NEUTRAL FREE-RADICAL CONDITIONS

Under mild and neutral free radical conditions, an alpha,beta-unsatura ted ketone reacted with tributyltin hydride to produce an intermediate resonance-stabilized allylic O-stannyl ketyl. Upon subsequent hydroge n atom abstraction, a tin(IV) enolate was afforded which could be quen ched with a variety of electrophiles and form new carbon-carbon bonds. Aldehydes react to produce aldol-type products and both intramolecula r and intermolecular carbonyl addition reactions were investigated usi ng this strategy. Using similar methodology, the tin(TV) enolate could be quenched in the presence of HMPA with various alkyl halides and al pha,beta-unsaturated carbonyl compounds (Michael accepters) to yield a lkylated products in good yields. These reactions represent a very mil d regioselective alternative to metal enolate formation which usually requires strong bases such as LDA or strongly reductive dissolving met al conditions to achieve success. New carbon skeletons for natural pro duct synthesis can be readily constructed using this chemically neutra l approach.