Reported herein is an effective strategy for oxidative cross-coupling of indoles with various aldehydes. The strategy is based on a two-step transformation via a well-known Mannich-type reaction and a C–N bond cleavage for carbonyl introduction. The key step—the C–N bond cleavage of the Mannich product—was enabled by electrochemistry. This strategy (with over 40 examples) ensures excellent functional-group