Access to benzo-fused nine-membered heterocyclic alkenes with a trifluoromethyl carbinol moiety via a double decarboxylative formal ring-expansion process under palladium catalysis

摘要

Direct access to pharmaceutically attractive benzo-fused nine-membered heterocyclic alkenes >3 with a trifluoromethyl carbinol moiety was achieved via a palladium-catalyzed double-decarboxylative formal ring-expansion process from six-membered trifluoromethyl benzo[d][1,3]oxazinones >1 to nine-membered trifluoromethyl benzo[c][1,5]oxazonines >3 in the presence of vinylethylene carbonates >2. Generation of a Pd-π-allyl zwitterionic intermediate was proposed in the catalytic cycle. The trifluoromethyl group in the benzoxazinanones >1 plays an important role throughout the transformation. Diastereoselective chemical transformations of products >3 were also demonstrated.