On the regioselectivity of the reaction of N-methoxycarbonylpyridinium chloride with Grignard reagents: highly regioselective synthesis of 2-substituted N-methoxycarbonyl-1,2-dihydropyridines.
Whereas alkyl Grignardreagents undergo 1,2- and 1,4-additions to N-methoxycarbonylpyridinium chloride in a variable ratio, alkenyl and alkynyl Grignardreagents do the exclusive 1,2-addition to afford 2-substituted N-methoxycarbonyl-1,2-dihydropyridines in fair to excellent yields.
Highly Regioselective α-Addition of Alkynyl and Alkenyl Grignard Reagents to 1-Alkoxycarbonylpyridinium Salts and Its Application to Synthesis of 1-Azabicycloalkanes and (±)-Solenopsin A
Nucleophilic addition of a variety of alkynyl and alkenyl Grignardreagents to 1-methoxycarbonylpyridinium chloride takes place at the α-position in a highly regioselective manner to give 2-substituted 1-methoxycarbonyl-1,2-dihydropyridines exclusively, while, with alkyl Grignardreagents, a lack of the regioselectivity is observed. These results may be explained by the HSAB principle. The high α-regioselectivity