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Synfacts 2006(10): 0999-0999  
DOI: 10.1055/s-2006-949353
Synthesis of Heterocycles
© Georg Thieme Verlag Stuttgart · New York

Diastereoselective Routes to Thiazines, Oxazines and Pyranopyrimidines

Contributor(s): Victor Snieckus, Heiko Scharl
Y. Zhu, S. Huang, J. Wan, L. Yan, Y. Pan*, A. Wu*
Zhejiang University, Hangzhou and Central China Normal University, Wuhan, P. R. of China
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Publication History

Publication Date:
21 September 2006 (online)

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Significance

Starting with the same two components, aldehydes and ureas/thioureas, two comparative methods for the construction of thiazines, oxazines and hexahydropyrano[2,3-d]pyrimidines are reported. In one sequence, the third component, an alkene, completes a [4+2] cycloaddition approach while in the other path dihydropyran is added to effect a Biginelli-type reaction. Both sequences require TMSCl and proceed in good yields and high overall diastereoselectivity. The formation of thiazines and oxazines is proposed to proceed via initial generation of an N-acyliminium species, which undergoes Diels-Alder reaction with the added alkene.