Quinazolines. Part XV. Hexahydro- and octahydro-quinazolines

Abstract

3,4,5,6,7,8-Hexahydroquinazoline, obtained by catalytic reduction of 5,6,7,8-tetrahydroquinazoline, was slowly oxidised by air to the starting material in chloroform solution, but in aqueous alkali it was degraded to 2-formamidomethylcyclohexanone. trans-4a,5,6,7,8,8a-Hexahydroquinazolin-4(1 - or 3-H)-one was shown to be a tautomeric mixture of the (1H)-one (20%) and (3H)-one (80%) in pH 9·2 aqueous buffer by comparing the u.v. spectrum with those of authentic 1- and 3-methyl derivatives. The preparations of cis- and trans-3,4,4a,5,6,7,8,8a-octahydroquinazoline hydrochlorides, 2-amino-3,4,4a,5,6,7,8,8a-octahydroquinazolin-4-ones, 2-amino-3,4,4a,5,6,7,8,8a-octahydroquinazoline salts, 2-oxo(1H) and 2-thio(1H)3,4,4a,5,6,7,8,8a-octahydroquinazolines, 1,2,4a,5,6,7,8,8a-octahydroquinazolin-4(3H)ones; cis-4a,5,6,7,8,8a-hexahydroquinazolin-4(3H)one, cis-2-amino-4,5-dihydro-4,5-tetramethylene-1,3(6H)-oxazine and thiazine, and cis-2,3,4,5-tetrahydro-2-oxo-4,5-tetramethylene-1,3(6H)-oxazine are described. The ¹H n.m.r. spectra of cis- and trans-octahydroquinazolines show spectral patterns for the 4,4a,5,6,7,8 and 8a-protons which are similar to those of cis- and trans-decahydroquinazolines respectively and are characteristic of the stereochemistry.