Regioselective Reactions of Organozinc Reagents with 2,4-Dichloroquinoline and 5,7-Dichloropyrazolo[1,5-<i>a</i>]pyrimidine
作者:Takeshi Shiota、Teruo Yamamori
DOI:10.1021/jo981423a
日期:1999.1.1
Strategies for controlling the regioselective reactions between 2,4-dichloroquinoline and organozinc reagents are described. 2,4-Dichloroquinoline has been found to react with benzylic zinc and phenylzinc reagents in the presence of catalytic amounts of palladium complexes to exclusively give a-substituted products. Several metal salts were examined as an additive for gamma-selective coupling reactions. The most effective additive for selective coupling reaction at the gamma-position has been found to be LiCl. These conditions for alpha- or gamma-selective coupling reactions were applied to the reaction between 5,7-dichloropyrazolo[1,5-alpha]pyrimidine and a biphenylmethylzinc reagent in the synthesis of the angiotensin II receptor antagonists. This regioselectivity should be generally applicable to other alpha,gamma-dichloroazine systems.