TOTAL SYNTHESES OF CLAVINE ALKALOIDS BY AN INTRAMOLECULAR NITRONE-OLEFIN CYCLOADDITION REACTION

Article abstract of DOI:10.1016/S0040-4020(01)88608-7

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 percent, 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.