Stereochemical studies 98. Saturated heterocycles 100. Synthesis of stereoisomeric 2-ethylimino-3,1-perhydrobenzoxazines and benzothiazines

Abstract

With ethyl isothiocyanate, the stereoisomericcis- andtrans-2-hydroxymethyl-1-cyclohexylamines and theirN-methyl andN-benzyl derivatives (4 a–c,5 a–c) furnished the corresponding thiocarbamates (6 a–c,7 a–c). Treatment of compounds6 and7 with methyl iodide and subsequent alkali treatment afforded 3,1-perhydrobenzoxazines8 a–c,9 a–c, while cyclization of compounds6 and7 to the 3,1-perhydrobenzothiazines10 a–c,11 a–c was performed with HCl. It was found that the predominant conformation of theN-unsubstitutedcis isomers8 a and10 a is theN-inside form, while theN-substituted derivatives8 b,c and10 b,c have theN-outside preferred conformation.