Thermolysis of the 1a,1b,6b,6c-tetrahydro-azirino[2′,3′:3,4]cyclobuta[1,2-b][1]benzofurans (3) results in ring transformations to from the benzofuro[2,3-b]pyrroles (5) and their [3,2-b]-isomers (6).
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Kurita et al. (1987) studied this question.