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 η 3 ‐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 .