1,3-Dipolar character of six-membered aromatic rings. Part 49. 3-Oxido-1-(4-pyridyl)pyridinium, 3-oxido-1-(2-pyridyl)pyridinium, 3-oxido-1-(quinoxolin-2-yl)pyridinium, 3-oxido-1-(5,6-diphenyl-1,2,4-triazin-3-yl)pyridinium, and 3-oxido-1-(5-phenyl-1,2,4-triazin-3-yl)pyridinium

Abstract

The title betaines are prepared: the two triazinyl betaines undergo spontaneous thermal dimerisation, and all add a variety of 2π, 4π, and/or 6π dipolarophiles. The regio- and stereo-chemistry of the addition are elucidated and rationalised. The pyridyl adducts undergo quaternisation and ring opening to tropolones.