Regioselectivity Tsuji-Trost reaction

Pd(0)-catalyzed allylations of 4(5)-nitroimidazole, 2-methyl-4(5)-nitroimidazole, 4(5)-bromoimidazole and 4(5)-methoxyimidazole resulted in complicated mixtures, which did not necessarily reflect the tautomeric ratios of the starting material [7], For example, poor regioselectivity for the products (70 and 71) was observed in the Tsuji-Trost reaction of 4(5)-bromoimidazole with cinnamyl carbonate. However, the same reaction with 4(5)-nitroimidazole and 2-methyl-4(5)-nitroimidazole led predominantly to the l-allylation products. In addition, removal of the 77-imidazole allyl groups can be selectively effected under mild conditions by Pd-catalyzed ic-allyl chemistry [55],... 

Scheme 5-6. Regioselectivity issues in the Tsuji-Trost reaction. ...

Transition metal-catalyzed allylic substitution reactions with carbon nucleophiles are among the most important carbon-carbon bond formation methods in modem organic synthesis, because of their broad substrate scope under mild reaction conditions. In addition, they are applicable to enantioselective reactions, as well as exhibiting versatility towards the alkene functionality adjacent to the chiral centre for stereoselective derivatization. Tsuji-Trost allylic substitution, involving a (Ti-allyl) metal intermediate, has provided a particular advance in this regard [34, 35]. Most recently, Sawamura et al. [36, 37] have improved the regioselectivity of this reaction with unsymmetrically substituted allylic esters, and thus opened a new approach to sertraline. 

The exterior surface of the mesoporous support was first deactivated by treatment with PhaSiCk under non-diffusive conditions. The inner walls of the materials were then functionalised with 3- (5)-l-[(/ )-r,2-bisdiphenyl-phosphino)ferrocenyl]ethyl-A/,Ar-dimethylethylenediamino propylsilane chains. The mesoporous chiral catalyst obtained on reaction of with PdCl2, revealed higher regioselectivity (50%) and enantioselectivity (99%) in the Trost-Tsuji reaction than the same catalytic site bound on non porous high-area silica (values in brackets on Fig. 1). 

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