Silver-catalyzed [4+3] cycloaddition of 1,3-dienes with alkenyl-N-triftosylhydrazones: a practical approach to 1,4-cycloheptadienes

The first formal [4 + 3] cycloaddition of 1,3-dienes with alkenyl-N-sulfonylhydrazones has been achieved employing easily decomposable alkenyl-N-triftosylhydrazones in the presence of a silver catalyst. A series of acyclic and cyclic 1,3-dienes reacted effectively with silver(i) non-acceptor vinyl carbenes, including challenging alkyl- and alkenyl-substituted substrates, producing a broad spectrum of 1,4-cycloheptadienes with high yields and predictable stereochemistry. The products resulting from the transformation described herein 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.