Palladium-Catalyzed Umpolung Type-II Cyclization of Allylic Carbonate-Aldehydes Leading to 3-Methylenecycloalkanol Derivatives

Palladium-catalyzed umpolung type-II cyclization of allylic carbonate-aldehydes leading to 3-methylenecycloalkanol derivatives was developed. The formate reductant was effective for the cyclization without causing a reduction of the η³-allylpalladium intermediate. One-pot decarboxylative allylation of aldehyde-containing malonate with 2-[(acetyloxy)methyl]-2-propenyl methyl carbonate followed by the cyclization of the allyl acetate-aldehyde formed in situ was also achieved. The high diastereoselectivities observed in the cyclization of branched substrates indicates that a chair-chair transition state should be involved. Based on the presumed transition state, we could predict the enantioselectivity of the cyclization using SEGPHOS as a chiral diphosphine ligand and obtain optically active alcohols in up to 95:5 er. (Figure presented.).