An Efficient and Simple Synthesis of 3,4,5,6-Tetrahydro-2H-1,2-oxazines by Sodium Cyanoborohydride Reduction of 5,6-Dihydro-4H-1,2-oxazines

Reinhold Zimmer; Thomas Arnold; Kai Homann; Hans-Ulrich Reissig

doi:10.1055/s-1994-25636

Synthesis 1994; 1994(10): 1050-1056
DOI: 10.1055/s-1994-25636

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An Efficient and Simple Synthesis of 3,4,5,6-Tetrahydro-2H-1,2-oxazines by Sodium Cyanoborohydride Reduction of 5,6-Dihydro-4H-1,2-oxazines

Reinhold Zimmer^* , Thomas Arnold, Kai Homann, Hans-Ulrich Reissig

^*Institut für Organische Chemie der Technischen Universität Dresden, Mommsenstrasse 13, D-01062 Dresden, Germany

Abstract

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3,4,5,6-Tetrahydro-2H-1,2-oxazines are prepared by reduction of the corresponding 5,6-dihydro-4H-1,2-oxazines with sodium cyanoborohydride as the reducing agent in acetic acid. This reaction gives the 3,5-disubstituted compounds 2a-c, 2f-g, and 5a,b with good to excellent cis selectivities, while a 3,6-disubstituted 1,2-oxazine leads to a trans configurated product as the major isomer. Under the same reaction conditions the bicyclic heterocycle 14 affords two products, the expected compound 15 and the cyclopentenol derivative 16 as a byproduct. Also, the formation of trifluoromethylated ketoximes 18 and 21 starting from the precursors 17 and 19 is described.

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