Compounds with bridgehead nitrogen. Part 54. The stereochemistry of some derivatives of perhydrothiazolo[3,4-a]pyridine and the synthesis of 9-methylperhydro-3,8-methano-1,3-thiazocines

Abstract

The position of conformational equilibria (CDCl₃ solution; 298 K) of perhydrothiazolo[3,4-a]pyridine and the corresponding 6-ethyl-substituted derivatives have been determined by ¹H and ¹³C n.m.r. spectroscopy. The reported synthesis of the 1-methylperhydrothiazolo[3,4-a]pyridines via 1-bromo-1-(2-piperidyl)ethane hydrobromide gave in addition the isomeric 9-methylperhydro-3,8-methano-1,3thiazocines. Contrary to an earlier report trans-(1H,8aH)-1-methylperhydrothiazolo[3,4-a]pyridine was found to adopt an 87%trans-fused ⇌ 13%cis-fused conformational equilibrium (CDCl₃; 193 K).