Diyne conjugation cyclotrimerization

Like simple alkynes, conjugated diynes undergo cyclotrimerization in the presence of transition metal catalysts, but whereas simple alkynes give symmetrically substituted benzenes almost exclusively, diynes give symmetrical (256) and unsymmetrical... 

Another type of benzannulation, which might be related to the benzannulation of conjugated enynes, is the Pd-catalyzed cyclotrimerization of 1,3-diynes (Scheme 1,3-Diynes cyclotrimerize in the presence of a Pd catalyst to give 1,3.5-trisubstituted benzene derivatives. In this reaction, too, the regioselectivity is perfectly controlled as shown in Scheme 4, and other products were never isolated. The reaction of various diynes is summarized in Table 7. Some functional groups such as olefins and ether linkages may be present in the side chain. An example for the cross-cyclotrimerization of a diyne and an aUcyne has also been reported (Scheme... 

Heptadiyne leads to a polymer that possesses a system of conjugated double bonds (11-41) (153, 154). The structural assignment was based on chemical and spectroscopic evidence. However, its correctness was questioned by Hubert and Dale (68). These workers interpreted the polymerization of unconjugated diynes, HC=C(CH2) C CH, as a poly(cyclotrimerization) rather than a cyclopolymerization, The trimerization of monoacetylenes in the presence of Ziegler catalysts is well known (148). 

The cyclopentadienylcobalt complexes CpCo(L)n are also good catalysts for co-cyclotrimerization of diynes with alkenes [79a]. Recently, it has been shown that the similar catalytic activity is exhibited by the ruthenium complex 106, which efficiently catalyzed cycloaddition of diynes with cyclic alkenes to the conjugated cyclohexadienes 174 (Scheme 77) [112]. 

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