Silver-Catalyzed [4+3] Cycloaddition of 1,3-Dienes with Vinyl-N-triftosylhydrazones: A Practical Approach to 1,4-Cycloheptadienes

The first formal [4+3] cycloaddition of 1,3-dienes with vinyl-N-sulfonylhydrazones has been achieved by virtue of easily decomposable vinyl-N-triftosylhydrazones in the presence of silver catalysis. A series of acyclic and cyclic 1,3-dienes reacted effectively with silver(I) non-acceptor vinyl carbenes, including alkyl- and alkenyl-substituted carbenes, which are notoriously challenging, producing a broad spectrum of 1,4-cycloheptadienes with high yield and predictable stereochemistry. The products resulting from the herein described transformation include bridged and fused polycyclic systems, as well as the natural product dictyopterene C' and its isomer ectocarpene. The reaction mechanism and the origin of stereoselectivity were investigated via experimental work and density functional theory calculations.