The First Optically Active Spirosulfurane Oxides: Stereoselective Syntheses and Racemization Processes

Abstract

Syntheses of optically active organosulfur derivatives having a trigonal bipyramidal structure are of a great interest either from the the oretical or from the stereochemical points of view. Althought he first optically active sulfurane, (+)-l-chloro-3,3-dimethyl-l-phenyl 1|3H-2,l-benzoxathiole| was reported as early as 1975¹, the first optically active spirosulfuranes have only recently been prepared either by an asymmetric dehydration approach² or by the stereo selective dehydration of the suitably constructed, optically active, orto-substituted diaryl sulfoxides. Althought he first attempt to synthetize optically active sulfurane oxide was reported as early as 1978⁴, such structures have not been isolated in enantiomeric forms until now. Having in hands optically active spirosulfuranes 1a,b^2,5 and knowing details of their thermal and acid-catalyzed racemization it was reasonable to expect that the corresponding sulfurane oxides 2a,b should be isolated in optically active form a tambient temperature.