Benzannulation, enyne/diyne conjugation

Saito S, Yamamoto Y (2002) Palladium-Catalyzed Benzannulation Reactions of Conjugated Enynes and Diynes. In Negishi E, de Meijere A (eds) Handbook of Organopalladium Chemistry for Organic Synthesis. Wiley, New York, p 1635... 

IV.10.2 Palladium-Catalyzed Benzannulation Reactions of Conjugated Enynes and Diynes... 

Saito, S. and Yamamoto, Y. (2002) Palladium-catalyzed benzannulation reactions of conjugated enynes and diynes, in Handbook of Organopalladium Chemistry for Organic Synthesis (eds E. Negishi and de A. Meijere), John Wiley Sons, New York, p. 124. 

Gevorgyan, V., Takeda, A., Homma, M., Sadayori, N., Radhakrishnan, U. and Yamamoto, Y. (1999) Palladium-catalyzed [4-1-2] cross-benzannulation reaction of conjugated enynes with diynes and triynes. Journal of the American Chemical Society, 121(27), 6391-6402. 

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... 

D. [4 + 2] ANNULATION OF CONJUGATED ENYNES WITH DIYNES (CROSS-BENZANNULATION)... 

TABLE 9. Pd-Catalyzed Cross-Benzannulation of Conjugated Enynes with Diynes (2)... 

Although a mechanism of the above palladium-catalyzed cross-benzannulation between conjugated enynes and diynes is not perfectly understood, the reaction may proceed via not a concerted mechanism but a stepwise mechanism [48]. 

The Pd(0)-catalysed 4 -i- 2-cross-benzannulations of conjugated enynes (167) with diynes (166) and triynes yield substituted benzene derivatives (168) (Scheme 64). " Monosubstituted conjugated enynes readily undergo 4 - - 2-homodimerization in the presence of Pd catalyst to produce 4,o - and 2,6-disubstituted styrenes. ... 

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