Synthesis of azepane-fused pyrano[3,2- b ]indoles by Lewis acid-catalysed oxa Diels-Alder reactions.

The dihydroazepino[1,2- a ]indole diones 3 are tricyclic oxindole-type enones which are readily accessible by catalytic photooxygenation of cyclohepta[ b ]indoles 1 followed by dehydration. Lewis acid-catalysed oxa Diels-Alder reactions of enones 3 with enol ethers 4 were developed that lead to novel tetracyclic azepane-fused pyrano[3,2- b ]indoles 5, with high stereoselectivity and under mild reaction conditions.