Bis-7t-allylpalladium

Formation of a bis-allylated product of 4-nitrobenzoyl chloride by the reaction with allyltrimethyltin in the presence of a benzylpalladium(ll) complex was observed by Stille and co-workers in 1983.4 Trost and King also reported allylation of aldehydes by allyltin reagents in 1990.456 However, the precise mechanism was unclear until the extended studies were performed by Yamamoto and co-workers since 1995.4S7,4S7a 4S7 Aldehydes and imines react with allyltin reagents in the presence of a palladium catalyst (Equations (95) and (96)), and imines are chemoselectively allylated in the presence of aldehydes (Equation (97)).4S7,4S7l 4 b Mechanistic studies using NMR spectroscopy proved that bis-7t-allylpalladium complex 203 is a key nucleophilic intermediate (Figure 3). 

A plausible mechanism for this asymmetric allylation has been formulated (Fig. 7). The first step involves the transmetallation of allyltributylstannane to palladium. The resulting bis-7t-allylpalladium complex 69 would react with im-ine 67 to give the 7t-allylpalladium complex 70 this coordination stage is the key step for the asymmetric induction observed in this reaction. The addition step would produce the 7t-allylpalladium amide 71, and another transmetallation of allyltributylstannane to palladium would lead to the formation of the desired product and the regeneration of complex 69. 

The carbopalladation of an aryne with a bis-7t-allylpalladium complex was shown to be a key step in the catalytic cycle. This protocol was, however, limited due to a lack of chemoselectivity since, if different allyl groups from aHyl chloride and an allylstannane were employed, then a mixture of crossover products was obtained. 

Scheme 71).124 An intermediate 7t-allylpalladium species (60) is thought to effect this transformation and in this context it is significant that presynthesized bis[acetoxy(7,l, 2)- j-pinene)palladium(II)]12 5 reacts in a similar fashion, affording optically active 59 in comparable optical yield.124... 

S)-l is obtained from the bis(methyl carbonate) of (Z)-2-butene-l,4-diol and l,2-bis(tosyl-amino)ethane through a tandem pa]ladium(0)-catalyzed allylic substitution in the presence of (R)-BINAP (I) as chiral ligand79. Equilibration of the 7t-allylpalladium intermediates formed before the intramolecular nucleophilic attack is necessary for high enantioselectivity. Thus, only a racemic piperazine is produced in the reaction of the more nucleophilic l,2-bis(benzyl-amino)ethane with the diacetate of (Z)- or ( )-2-butene-l,4-diol. 

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