Bisallylpalladium intermediates

Allylation via Bisallylpalladium Intermediates As mentioned in Scheme 6.4, Yamamoto et al. [9] have shown that successive addition of an aUyl chloride and an allylstannane to a palladium(O) precursor generates a bisallylpalladium complex. This reaction can be employed under catalytic conditions and has led to many useful apphcations of allylstannanes in organic synthesis [80-82]. The aUyl moieties of bisallylpalladium complexes may undergo an allyl-aUyl couphng reaction, and thus, the process can be employed for syntheses of 1,5-dienes [82a]. Another interesting area involves reactions of electrophiles, such as aldehydes, imines (Scheme 6.19), and the Michael acceptors (Scheme 6.20) with bisallylpalladium intermediates [80-82b]. 

Scheme 6.19 Palladium-catalyzed allylation of aldehydes and imines via bisallylpalladium intermediates.

Yamamoto et al. [80c,d] described a catalytic asymmetric version of the allylation reaction of aldimines. In this process, a chiral bisallylpalladium intermediate is formed from an (IS)-a-(-)pinene-based monoallylpalladium complex (Scheme 6.22). Subsequently, this complex undergoes electrophilic attack by... 

Bisallylpalladium intermediates are generated starting from 1 and either a combination of allyl chloride and hexamethylditin (eq 41) or in the presence of allyltributylstannane and allyl chloride (eq 42). The catalytic reaction with an aldehyde as electrophile proceeds under mild conditions at 40 °C overnight and leads to the corresponding homoallylic alcohol (eq 41). The tandem version implying the use of allyltributylstannane derivative is accompanied by a cyclization reaction leading to 5-exo and 6-endo cyclic ethers (eq 42). The exolendo ratio highly depends on the substitution of the alkynyl chain. 

Support for this type of an intermediate has been found in the isolation of an f l,fj3-bisallylpalladium phosphine complex, (i/, j3-C3H5)2PdPR3 (R = CH3 and C6H,) by Jolly and co-workers (117). These complexes were found to insert C02 to form the palladium carboxylate (39), which upon addition of two equivalents of CO eliminated 2-propenyl-2-butenoate (40) [Eq. (47)]. 

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