A 7-MEMBERED-RING ALLENE DIMER - SYNTHESIS OF 1,2-BENZO-1,3,4-CYCLOHEPTATRIENE AND ATTEMPTED SYNTHESIS OF 1,2-BENZO-1,4,5-CYCLOHEPTATRIENE

7,7-Dibromo-3,4-benzobicyclo[4.1.0]heptane (6) and 7,7-dibromo-2,3-ben zobicyclo[4.1.0]heptane (14) have been synthesized and their silver io n-catalyzed reactions studied. Hydroxy alcohol 7a was converted to the corresponding vinyl bromide 10. Reaction of 10 with base gave the hyd rocarbon 12, instead of the expected allene 4. Hydroxy alcohol 15a was converted to the corresponding mesylate 20, but all attempts to reduc e 20 to the expected vinyl bromide 23 failed. Instead, unexpected ethe r 21 was obtained. Therefore, 15a was treated with PBr3 to give 22, wh ich upon treatment with LiAlH4 gave the vinyl bromide 23. Reaction of 23 'with potassium tert-butoxide produced strained bicyclic allene 5, which underwent a dimerization to give 24. Addition of tetracyanoethyl ene to dimer 24 resulted in the formation of 26, whose structure was i nvestigated by X-ray crystallography.