Tetrahedron

Alkoxynitrenium ion cyclisations: evidence for different mechanisms in the formation of benzoxazines and benzoxazepines

SA Glover, CA Rowbottom, AP Scott, JL Schoonraad

Index: Glover, Stephen A.; Rowbottom, Colleen A.; Scott, Anthony P.; Schoonraad, Johan L. Tetrahedron, 1990 , vol. 46, # 20 p. 7247 - 7262

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Citation Number: 29

Abstract

Deuterium labelling experiments and nmr studies indicate that cyclisations of N-acyl-N-(2- phenylethyloxy) nitrenium ions occur via direct attack at the ortho position to give 34-dihydro- 1 H-21-benzoxazines. In contrast N-acyl-N-(3-phenylpropyloxy) nitrenium ions cyclise to 1345-tetrahydro-21-benzoxazepines through ipso attack followed by 12-carbon migration. In both cases hydrogen circumambulation occurs in the sigma complex before aromatisation.