Phosphine-Catalyzed Crossed Rauhut-Currier-Type Coupling and [3 + 2]-Cycloaddition of 2-Alkylidene-3-oxindoles with Alkenes and Allenes to Access β,γ-Unsaturated Enones and Polycyclic Oxindoles.

Dihydroazepino[1,2-]indole diones are tricyclic -acyl-2-alkylidene-3-oxindole enones that readily engage in tertiary phosphine-catalyzed intermolecular coupling reactions with acceptor-substituted alkenes. In these reactions, the tricyclic α-substituted enones undergo an α-alkylation with concomitant formation of a quaternary stereocenter, as well as the installation of a new double bond within the seven-membered azepane ring. The organocatalytic reaction constitutes a special case of the crossed intermolecular Rauhut-Currier reaction as the presence of the α-substituent in the enones prohibits the formation of an α,β-unsaturated product, but instead, skipped β,γ-unsaturated enones are obtained.

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

The dihydroazepino[1,2-]indole diones 3 are tricyclic oxindole-type enones which are readily accessible by catalytic photooxygenation of cyclohepta[]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-]indoles 5, with high stereoselectivity and under mild reaction conditions.