An Approach to Cyclohepta[b]indoles through an Allenamide (4 + 3) Cycloaddition–Grignard Cyclization–Chugaev Elimination Sequence

A strategy for synthesizing highly functionalized cyclohepta­[b]­indoles through a concise (4 + 3) cycloaddition–cyclization–elimination sequence is described. The cycloaddition features nitrogen-stabilized oxyallyl cations derived from epoxidations of N-aryl-N-sulfonyl-substituted allenamides, while the cyclization and elimination employed an intramolecular Grignard addition and a one-step Chugaev process, respectively.