Synthesis of substituted tetrahydropyridines and M-hydroxybenzoic acids

A series of substituted 1,2,3,6- (5) and 1,2,5,6-tetrahydro-pyridines (6) have been synthesised via intramolecular 1,6-Michael addition of methoxycarbonyl-2,4-dienylamines (10). The kinetics of these reactions have been investigated and an explanation of substituent effects is advanced. Also a new route to m-hydroxybenzoic acids has been established by cyclisation of substituted hexa-3,4:5,6-dienoic acids.