Palladium-Catalyzed Enantioselective 1,3-Rearrangement of Racemic Allylic Sulfinates:  Asymmetric Synthesis of Allylic Sulfones and Kinetic Resolution of an Allylic Sulfinate

Described is an asymmetric synthesis of cyclic and acyclic allylic <i>S</i>-aryl and <i>S</i>-alkyl sulfones through a highly selective palladium(0)-catalyzed 1,3-rearrangement of racemic allylic sulfinates. Treatment of racemic cyclic and acyclic allylic <i>S</i>-tolyl- and <i>S</i>-<i>tert</i>-butylsulfinates with Pd<sub>2</sub>(dba)<sub>3</sub>·CHCl<sub>3</sub> as precatalyst and <i>N</i>,<i>N</i>‘-(1<i>R</i>,2<i>R</i>)-1,2-cyclohexanediylbis[2-(diphenylphosphino)benzamide] as ligand for the palladium atom afforded the corresponding isomeric allylic <i>S</i>-tolyl and <i>S</i>-<i>tert</i>-butyl sulfones of 93−99% ee in 82−96% yield. The rearrangement of the allylic sulfinates most likely proceeds in an intermolecular fashion via formation of a cationic π-allylpalladium complex and the sulfinate ion. The racemic allylic sulfinates were obtained from the corresponding racemic alcohols and racemic tolylsulfinyl chloride and racemic <i>tert</i>-butylsulfinyl chloride, respectively, in high yields. Rearrangement of the racemic <i>tert</i>-butylsulfinic acid 2-cyclooct-1-enyl ester with Pd<sub>2</sub>(dba)<sub>3</sub>·CHCl<sub>3</sub> and the bisphosphane was accompanied by a highly selective kinetic resolution of the substrate and gave at 50% conversion the (<i>R</i>)-configured sulfinate as mixture of the <i>S</i><sub>S</sub> and <i>R</i><sub>S</sub> diastereomers of 92% ee and 85% ee and the (<i>S</i>)-configured 3-<i>tert</i>-butylsulfonyl cyclooctene sulfone <b>15a</b> with 98% ee in almost quantitative yields.