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Transition metal- and acid-induced transformations of 6-siloxy-substituted 5,6-dihydro-4H-1,2-oxazines: Preparation of pyrroles, nitrones, 1,4-dicarbonyl compounds and derivatives thereof

✍ Scribed by Hippeli, Claudia ;Zimmer, Reinhold ;Reißig, Hans-Ulrich

Publisher: John Wiley and Sons
Year: 1990
Tongue: English
Weight: 566 KB
Volume: 1990
Category: Article
ISSN: 0947-3440
DOI: 10.1002/jlac.199019900189

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✦ Synopsis

Abstract

A variety of 6‐siloxy‐substituted 5,6‐dihydro‐4__H__‐1,2‐oxazines (abbreviation: 1,2‐oxazines) 1, 3 could be transformed into di‐ and trisubstituted pyrroles 2, 4 by means of molybdenum hexacarbonyl. The mechanism of this deoxygenating ring contraction is discussed. With two bicyclic 1,2‐oxazines an acid‐catalyzed fragmentation affording α‐methylenecycloalkanones 7 has been observed, while other 1,2‐oxazines rearrange in methanolic acid to give nitrones 9, 10. The desilylation of 6‐siloxy‐substituted 1,2‐oxazines 1, 3 employing NEt~3~ · 3 HF is a very general and smooth process providing 6‐hydroxy‐1,2‐oxazines 11, 12 or their corresponding acyclic tautomers 13, 14 in high yields. For two examples of 11 deoximations by use of formalin could be achieved with moderate efficiency giving 1,4‐dicarbonyl compounds 15.

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