Metalation of Hantzsch esters and mixed amide esters: a general route to C-2 functionalized 1,4-dihydropyridines
作者:Graham S. Poindexter、Joseph F. Licause、Peter L. Dolan、Michael A. Foley、Charles M. Combs
DOI:10.1021/jo00067a012
日期:1993.7
1,4-Dihydropyridine (Hantzsch) diesters 3a-e readily undergo metalation at the C-2 methyl (vinylogous ester) position on treatment with alkyllithium bases. The resulting anion intermediates can be treated with electrophilic reagents to afford 1,4-dihydropyridine products that have been chemically elaborated at the C-2 methyl position. The methodology permits a variety of electrophilic functionalities to be regiospecifically introduced at the C-2 methyl position of 1,4-dihydropyridines. Deuterium distribution studies with mixed dihydropyridine amide esters 20a and 20b having nonequivalent C-2 and C-6 methyl groups indicate specific metalation occurs at the C-2 methyl (vinylogous ester) position. Tri- and tetraanion formation is also possible at both vinylogous methyl and NH positions when the metalation reactions are performed with excess equivalents of n-BuLi or 8-BuLi bases.