The racemic ergot alkaloids chanoclavine I (1) and 6,7-secoagroclavine (4) have been synthesized stereoselectively from indole-4-carboxaldehyde (7) in overall yields of 14 and 13%, respectively. Further syntheses of isochanoclavine I (2), paliclavine (5) and costaclavine (6), via the same isoxazolidine 18 are described. The key step 16→18 (Scheme 4) involves a transient nitrone 17 which undergoes a kinetically controlled, regio- and stereoselective intramolecular cycloaddition to a 1,2-disubstituted olefinic bond.