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Synthesis of some benzoxaza and benzodioxaza heterocycles: Use of the Meisenheimer rearrangement route to fused medium-ring systems


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Gunawardana, IWK 1982 , 'Synthesis of some benzoxaza and benzodioxaza heterocycles: Use of the Meisenheimer rearrangement route to fused medium-ring systems', Research Master thesis, University of Tasmania.

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The aim of this work was to prepare examples of benzodioxazocine
and benzodioxazonine ring systems by the Meisenheimer rearrangement of
the N-oxides of related benzoxaza systems.
The 1,4-benzoxazepine and 1,5-benzoxazocine derivatives required
as starting materials were prepared by two different ring construction
methods, viz. the Bischler-Napieralski cyclization and a C-N type
condensation. For example, 8-methoxy-5-phenyl-2,3-dihydro-1,4-
benzoxazepine was obtained by the Bischler-Napieralski cyclization of
an amide precursor. Three other 1,4-benzoxazepine derivatives and
9-methoxy-6-phenyl-3,4-dihydro-2H-1,5-benzoxazocine were similarly
prepared (Chapters 2 and 3).
A C-N type ring construction method was employed to prepare
5-phenyl-2,3-dihydro-1,4-benzoxazepine and its 7-chloro analogue. In
these cases the precursors were amino-ketones.All these cyclic imines were then converted to the corresponding
N-methyl amines by quaternization and reduction. These amines were
converted to their N-oxides for use in the Meisenheimer rearrangement.
The Meisenheimer rearrangement of 1,4-benzoxazepine-N-oxides
proceeded smoothly giving rise to the corresponding 1,5,4-benzodioxazocine
derivatives in high yields. For example, 9-methoxy-4-methyl-6-phenyl-
3,4-dihydro-2H,6H-1,5,4-benzodioxazocine was prepared from 8-methoxy-
4-methyl-5-phenyl-2,3,4,5-tetrahydro-1,4-benzoxazepine-N-oxide. Five
analogous 1,5,4-benzodioxazocines were similarly prepared (Chapter 4).
However, when the 1,5-benzoxazocine-N-oxide derivative was subjected
to this rearrangement at about 10°, only decomposition products,
including hydroxylamines, were obtained. At lower temperatures (-5°-0°)
the Meisenheimer rearrangement of this N-oxide gave the expected ring
enlarged product, 10-methoxy-5-methyl-7-phenyl-2,3,4,5-tetrahydro-7// 1,6,5-benzodioxazonine in 50% yield. The 1,5,4-benzodioxazocine and
1,6,5-benzodioxazonine ring systems have not been described previously.

Item Type: Thesis - Research Master
Authors/Creators:Gunawardana, IWK
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