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 S-aryl and S-alkyl sulfones through a highly selective palladium(0)-catalyzed 1,3-rearrangement of racemic allylic sulfinates. Treatment of racemic cyclic and acyclic allylic S-tolyl- and S-tert-butylsulfinates with Pd₂(dba)₃·CHCl₃ as precatalyst and N,N‘-(1R,2R)-1,2-cyclohexanediylbis[2-(diphenylphosphino)benzamide] as ligand for the palladium atom afforded the corresponding isomeric allylic S-tolyl and S-tert-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 tert-butylsulfinyl chloride, respectively, in high yields. Rearrangement of the racemic tert-butylsulfinic acid 2-cyclooct-1-enyl ester with Pd₂(dba)₃·CHCl₃ and the bisphosphane was accompanied by a highly selective kinetic resolution of the substrate and gave at 50% conversion the (R)-configured sulfinate as mixture of the S_S and R_S diastereomers of 92% ee and 85% ee and the (S)-configured 3-tert-butylsulfonyl cyclooctene sulfone 15a with 98% ee in almost quantitative yields.