Reaction of Thioketones with ( R )‐2‐Vinyloxirane: Regio‐ and Stereoselective Formation of ( S )‐4‐Vinyl‐1,3‐oxathiolanes

The reactions of 4,4'‐dimethoxythiobenzophenone ( 1 ), 9 H ‐xanthene‐9‐thione ( 2 ), and adamantane‐2‐thione ( 3 ) with ( R )‐2‐vinyloxirane [( R )‐ 6 ] in the presence of SiO 2 in anhydrous CH 2 Cl 2 at 0 °C or room temperature afforded the corresponding 4‐vinyl‐1,3‐oxathiolane derivatives ( S )‐ 7 , ( S )‐ 9 , and ( S )‐ 11 , respectively. The analogous BF 3 ‐catalyzed reactions of ( R )‐ 6 with 1,1,3,3‐tetramethylindane‐2‐thione ( 4 ) and 2,2,4,4‐tetramethyl‐3‐thioxocyclobutanone ( 5 ) in anhydrous CH 2 Cl 2 at –65 °C or –78 °C yielded the corresponding spirocyclic 1,3‐oxathiolanes ( S )‐ 12 and ( S )‐ 14 , respectively. The structures of ( S )‐ 9 and ( S )‐ 12 were established by X‐ray crystallography. In all cases, the nucleophilic thiocarbonyl S atom attacked predominantly C(2) of the Lewis acid‐activated ( R )‐2‐vinyloxirane ring with inversion of the configuration through an S N 2‐type mechanism. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)