Butyllithium, reaction with 1,3-dioxolanes

A general methodology for the construction of quaternary carbon atoms at the carbonyl carbon of ketones has been successfully exploited for the facile synthesis of ( )-lycoramine (299) (Scheme 30) (165). Thus, the O-allylated o-vanillin 322 was allowed to react with vinyl magnesium bromide followed by Jones oxidation, and the acid-catalyzed addition of benzyl IV-methylcarbamate to the intermediate a,(3-unsaturated ketone furnished 323. Wadsworth-Emmons olefination of 323 with the anion derived from diethyl[(benzylideneami-no)methyl]phosphonate (BAMP) provided the 2-azadiene 324. The subsequent regioselective addition of n-butyllithium to 324 delivered a metalloenamine that suffered alkylation with 2-(2-bromoethyl)-2-methyl-l,3-dioxolane to give, after acid-catalyzed hydrolysis of the imine and ketal moieties, the 8-keto aldehyde 325. Base-catalyzed cycloaldolization and dehydration of 325 then provided the 4,4-disubstituted cyclohexenone 326. The entire sequence of reactions involved in the conversion of 323 to 326 proceeded in very good overall yield and in one pot. 

Selective attack of cyclopropyllithium on the aldehyde moiety has been realized by performing the reaction in the presence of an optically active complex. The best result was obtained when cyclopropyllithium, generated by treating bromocyclopropane with rerf-butyllithium, was reacted with nonanal in the presence of (4, 5/ )-2-rerr-butyl-a,a,a, a -tetraphenyl-l,3-dioxolane-4,5-dimethanol A 1-cyclopropylnonan-l-ol was obtained in 81% with 40% ee. ... 

---