Conjugate addition cross-coupling reactions

When the metallic additive to the intermediate 374 was zinc dihalide (or another Lewis acid, such as aluminum trichloride, iron trichloride or boron trifluoride), a conjugate addition to electrophilic olefins affords 381 . In the case of the lithium-zinc transmetallation, a palladium-catalyzed Negishi cross-coupling reaction with aryl bromides or iodides allowed the preparation of arylated componnds 384 ° in 26-77% yield. In addition, a Sn2 allylation of the mentioned zinc intermediates with reagents of type R CH=CHCH(R )X (X = chlorine, bromine) gave the corresponding compounds 385 in 52-68% yield. ... 

The 1,4-conjugate addition of triorganoindium to enones is promoted by a catalytic amount of Ni(COD)2 (Scheme 8.71) [100], Allylindium reagents can be used in Pd-catalyzed cross-coupling reaction with aryl halides (Scheme 8.72). The Pd-catalyzed allylic substitution of allyl carbonate produces 1,5-dienes (Scheme 8.73) [101]. The indium-mediated palladium-catalyzed Ullmann-type reductive coupling of aryl halides proceeds in aqueous media under air (Scheme 8.74) [102]. 

Enal-derived nickel-Jt-allyl complexes are efficient partners in cross-coupling reactions with alkenyl- and arylstannanes leading to products such as 39 (Scheme 23).P 1 As described for the aUylic ether derived complexes, the mechanism of the coupling process involves transmetalation followed by reductive elimination. The reaction is catal hic in nickel, unlike couplings of enals with allstoichiometric quantities of nickel. Many other variants of nickel-catalyzed conjugate additions may involve Ji-allyl complexes, but these are treated separately in a section on alkenes (Section 1.1.4.2) because the mechanism is poorly defined in most nickel-catalyzed conjugate additions. 

The formation of 2-alkenyl-substituted furans was observed in the palladium-catalyzed cross-coupling reactions between benzyl, aryl, or allyl bromides and conjugated ene-yne-ketones. This reaction involved oxidative addition, alkyne activation-cyclization, palladium carbene migratory insertion, P-hydride elimination, and catalyst regeneration (13JA13502). 

J.-E. Backvall, Palladium-Catalyzed 1,4-Additions to Conjugated Dienes, review in Metal-catalyzed Cross Coupling Reactions, Eds P. Stang and F. Diederich, WILEY-VCH, Weinham, 1998, pp. 339-385. 

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