The racemic alkaloids chanoclavine I (1) and isochanoclavine I (2) have been synthesized stereoselectively from indole-4-carbaldehyde (3) by a sequence of 11 operations in overall yields of 14% and 2.4%, respectively. The key step 6 → 8(Scheme 2) involves a transient nitrone 7 which undergoes a regio- and stereoselective intramolecular cycloaddition to a 1,2-disubstituted olefinic bond.