Thiazole constrained analogues of the thevinones: synthesis and structure

A simple synthesis of ring‐constrained endoethenomorphinans possessing 2′‐substituted thiazole ring 4–6 has been achieved by regio‐ and stereoselective Diels–Alder reaction of thiazolomorphinandienes 1–3 and methyl vinyl ketone in high yield (72, 64 and 87%, respectively). The structure of cycloaddition products was determined by high resolution mass spectrometry (HRMS), IR, 1D and 2D NMR techniques. Double‐pulsed field gradient spin‐echo–nOe and HMBC were found to be particularly powerful and indispensable tools in the exact structural elucidation of the presented new class of spatially constrained thevinones. Copyright © 2009 John Wiley & Sons, Ltd.