Studies in the Cycloproparene Series: Approaches to Bicyclo[5.1.0]octa-1,3,6-triene, a Cyclopropa-Fused Cycloheptatriene

Abstract

The dichloromethylene -bridged annulene (5) is available in four steps (47%) from 1,4,5,8-tetrahydronaphthalene (11) via the dibromide (15); the minor (5%) product of dehydrobromination of (15) is 2-bromo-9,9-dichloro-1,4-dihydro-4a,8a-methanonaphthalene (16). Dichlorocarbene adds to the norcaradiene form of (5) to give adduct (6) with 80% efficiency. Diene (6) resists both [π4+π2] cycloadditions and reductive dechlorination. Neither (5) nor parent 1,6-methano[10] annulene (18) adds methylene from Simmons-Smith cyclopropanation procedures.