An Improved Synthesis of Spiro [2.6]Nonatriene The Addition of Cycloheptatrienylidene to Ethylene

Abstract

A few years ago the synthesis of spiro [2.6]nona-4,6,8-triene (2) was accomplished in a multistep low overall yield sequence which began with the acid chloride of cyclopropane carboxylic acid.² A more direct route to 2 via the addition

of cycloheptatrienylidene (1) to ethylene seemed unlikely since at that time only highly electron deficient olefins such as dimethyl fumarate had been found to successfully trap this carbene.³ With the recent discovery that cycloheptatrienylidene adds to less deficient double bonds such as styrene⁴ and 1,3-pentadiene⁵, it was decided to explore its reaction with ethylene.