The steric configurations of (-)-galbelgin and galgravin (isomeric forms 111) have been investigated by fission of the tetrahydrofuran ring with sodium and ethanol in liquid ammonia, and examination of the products. Reduction of ( f)-1 : 2- (VII) and ( f)-3 : 4-dehydrogalbulin (VIII) by lithium and ammonia leads predominantly to ( -J-) -galbulin which accordingly has the configuration (I1 + its enantiomer) . The action of perchloric acid in acetic acid on galgravin and galbelgin has been investigated. We conclude that galgravin is probably (XII) and galbelgin probably (XIV) . (-)-Galcatin (I) * has been converted into (-)-galbulin (11).