Studies in the cycloproparene series: Halogenation and dehydrohalogenation of some 1a,9b-dihydrocyclopropa[l]phenanthrenes

Dehydrohalogenation of (1a,1aß,9aß)-1-chloro-1a,9b-dihydrocyclopropa [l]phenanthrene (4b) yields products by way of the corresponding dibenzobicyclohepta-2,4,6-triene (5b) whilst under solvolytic conditions the 7-t-butoxydibenzocyclohepta-1,3,5-triene (llb) is formed by cyclopropyl-allyl ring expansion. When subjected to bromination the cyclopropaphenanthrenes (4a,c) yield halophen-anthrenes(14a) and (15c) by cleavage of an external bond of the cyclopropane ring.