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 R-substituted products. Several metal salts were examined as an additive for γ-selective coupling reactions. The most effective additive for selective coupling reaction at the γ-position has been found to be LiCl. These conditions for Ror γ-selective coupling reactions were applied to the reaction between 5,7-dichloropyrazolo[1,5-a]pyrimidine and a biphenylmethylzinc reagent in the synthesis of the angiotensin II receptor antagonists. This regioselectivity should be generally applicable to other R,γ-dichloroazine systems.
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