Stereoselective Transformation of Cyclodecene-1,4-dione Systems, Derived from Steroids, to the Corresponding spiro-γ-lactones. A Semiempirical MO Study

The thermal and acid-catalyzed intramolecular rearrangement of the (Z)- and (E)-cyclodecene-1,4-dione compounds deriving from steroids, 2a,b and 3a,b, respectively, proceeds stereoselectively to give the corresponding configurationally different spiro-γ-lactone derivatives, the (5R,9R)-isomers 4a,b (from the (Z)-cyclodecenediones 2a,b) and the (5R,9S)-isomers 5a,b (from the (E)-cyclodecenediones 3a,b). The semiempirical MNDOAM1 and PM3 molecular orbital methods were applied to elucidate the possible mechanistic pathway of the observed intramolecular process leading to the spiro-γ-lactone structures