Enamines from formamides. Synthesis of 1,2,3,4-tetrahydro-1-substituted β-carbolines

Abstract

Pyridines and benzopyridines substituted with trimethylsilylmethyl groups, α or γ to the nitrogen atom, have been found to react with formamides by way of a Peterson reaction to form enamines. Trimethylsilylmethylbenzene behaved similarly. The enamines prepared from Nb-formyl-Na,Nb-dimethyltryptamine cyclized readily to β-carbolines. The reaction of formamides with lithiated 4-methylpyridines as a route to enamines was examined but proved to be less general and proceeded in lower yield than the route by way of the Peterson reaction. The nuclear magnetic resonance and mass spectra of the enamines and β-carbolines derived from 3 are discussed.