Enones reductive cross-coupling

Titanium A reductive cross-coupling of acrylonitriles CH2=CHCN with cyclo-hexenone and other enones, which connects the jS-carbons of both substrates, can be catalysed by Ti(III), generated from Cp2TiCl2 by reduction with zinc (in reminiscence of McMurry coupling). A plausible mechanism, involving a redox umpolung of the enone, has been proposed. " ... 

The latter process can even provide enantioselectivities over 99% in 1,4-additions to enones [437]. Very recently, cinnamaldehydes were found to give an anomalous selfconjugate reduction/cross-coupling tandem reaction [438], and arylboroxines reportedly undergo a catalytic asymmetric addition to N-tosylaryHmines [439]. Palladium and nickel catalysts promote similar additions of boronic adds onto unactivated alkynes [440], allenes [441], and 1,3-butadienes [442]. These new reactions of boronic acids are reviewed in detail in Chapter 4. 

The key step in a short and efficient synthesis of pleraplysillin-1 (127) is the palladium-catalyzed cross-coupling of vinylstannane 125 with vinyl triflate 126 (see Scheme 33). This synthesis is noteworthy in two respects. First, vinyl triflate 126 is generated regio-specifically from the kinetic enolate arising from a conjugate reduction of enone 124 the conjugate reduction of an enone is, in fact, a... 

In contrast to the typical palladium(0)-catalyzed cross-coupling reaction of vinyl triflates with organosilanes, this is an example of the reduction of an enone to an alkene by transfer of a proton instead of an alkyl moiety/ ... 

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]. 

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