Palladium-catalyzed coupling of 2,2t dihalobiaryls with metallated cyclopentenes. An easy synthesis for spiro[cyclopentene-1,9−[9H]fluorene]s

In the presence of palladium C8lalysts, one of the two carbons attached to halogen in 2,2'-diiodobipbenyl couples with unsaturated organometallics, after which the other adds to the newly incorporated double bond. Spiro(cyc1opentene-l,9'-(9H)f)s can be synthesized in this way. Since the combination of aryl (or vinyl) halides both with unsaturated organometallics by coupling 1 and with alkenes by addition and elimination (the Heck Reaction)2 are catalyzed by palladium reagents, it should be possible to prepare cyclic structures by using the former reaction to generate the substrate for the latter. Equations 1-4, which we report here, are the first examples of this sequence.3 We assume, using eq 1 as an illustration, that the key steps are those outlined in Scheme I. (Two moles of alkenylzinc chloride were used in eqs 1-3, and HI is probably consumed by the excess.) The synthesis in eq I, for which the zinc halide derivative was used because of its efficacy in couplings previously described,lM is considerably shorter than the classical sequence recently used to prepare the same structure. S It is also notable that the even though its formation causes benzene rings to clash, the same kind of product is formed by the analogous binaphthyl (eq 2).