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Catalytic Hydrogenation of 5,6‐Dihydro‐4 H ‐1,2‐oxazines Bearing a Functionalized Methylene Group at C‐3
Abstract The catalytic hydrogenation of readily available methyl 2‐(5,6‐dihydro‐4 H ‐1,2‐oxazin‐3‐yl)acetates 6 has been studied. Dihydrooxazines 6 without an alkoxy substituent at C‐6 under mild hydrogenation conditions in methanol produce a dynamic mixture of enamines 7 and tetrahydro‐2‐furanamine...
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Published in: | European journal of organic chemistry 2008-08, Vol.2008 (23), p.4025-4034 |
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Main Authors: | , , , , , |
Format: | Article |
Language: | English |
Citations: | Items that this one cites Items that cite this one |
Online Access: | Get full text |
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Summary: | Abstract
The catalytic hydrogenation of readily available methyl 2‐(5,6‐dihydro‐4
H
‐1,2‐oxazin‐3‐yl)acetates
6
has been studied. Dihydrooxazines
6
without an alkoxy substituent at C‐6 under mild hydrogenation conditions in methanol produce a dynamic mixture of enamines
7
and tetrahydro‐2‐furanamines
7′
(α + β). These products can be transformed into 1,4‐amino alcohols
8
under more robust hydrogenation conditions or into isomeric dihydrofurans
9
and
10
if the reduction is carried out in glacial acetic acid. Reduction of dihydrooxazines
6h
,
i
, which possess an alkoxy substituent at C‐6, under similar conditions affords pyrrolidine derivatives
12
,
13
and
14
. A general mechanistic scheme for the hydrogenation reaction that involves an initial N–O bond cleavage has been suggested. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008) |
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ISSN: | 1434-193X 1099-0690 |
DOI: | 10.1002/ejoc.200800288 |