Addition of dichloro- and dibromocarbene to 1,2-diphenylcyclobutenene

1,2-Diphenylcyclobutene (7) was reacted with dibromo-and dichlorocarbene, b oth generated via three different methods. 1,3-Diphenyl-2-halocyclopenta-1, 3-dienes 12 were isolated which result from addition of the dihalocarbenes to the cyclobutene double bond of 7. A cationic cyclopropyl-allyl rearrange ment (CCA) in gem-dihalobicyclopentanes 8 leads to 2,3-dihalocyclopentenes 9, which under the reaction conditions are dehydrohalogenated to 12. A seco nd carbene addition and rearrangement afford aromatic compounds 11 and 16.