Conjugate substitution arylation

Alkynes conjugated to a triple bond are very reactive systems toward hydrotelluration. The reaction occurs in a shorter reaction time when compared to the reactions commented above. In this case, even disubstituted triple bonds give vinylic tellurides in good yields.41,42,139 140 In the case of non-symmetrical diynes, an order of reactivity is established for the hydrotelluration of triple bonds of the enyne systems (terminal > propargylic > alkyl substituted > aryl substituted).140 This order of reactivity is reflected in the preferential formation of the vinylic tellurides shown in Scheme 39. 

A number of aryl halides and aryhnetals, especially those containing heteroatoms, are formally represented as a,/3-unsaturated carbonyl derivatives. Although their cross-coupling reactions may be formally classified as conjugate substitution processes, various requirements for these cases may be significantly different than in those cases discussed in Sects. B and C because of their aromatic nature. For this reason, specific examples of these reactions together with those of the reactions of quinone derivatives are discussed separately in Sect. D. 

TABLE 3. Pd-Catalyzed Homobenzannulation of 4-Substituted Conjugated Enynes (Aryl Group)... 

Conjugate Asymmetric Arylation of 3-Substituted a,P-unsaturated Carbonyl Compounds... 

Godt [181] coupled arylbutadiynylstannanes with substituted aryl iodides. Saalfrank et al. [182] allowed stannylalkynes or bis(trimethylstannyl)alkyne to react with bromoallenes to afford conjugated alkynylallenes or diastereomeric ynediaUenes. 

The palladium-catalyzed cross-[4+2] cycloaddition proceeded between conjugated enynes and diynes with excellent chemo- and regioselectivity to give densely substituted aryl acetylenes (Scheme 21.41) [47]. 

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