Pd-catalyzed asymmetric synthesis of allylic tert-butyl sulfones and sulfides: Kinetic resolution of the allylic substrate by a chiral Pd-complex

Abstract

The acyclic and cyclic allylic tert-butyl sulfones 3, ent- 3, 11a, 11b and 15a–c of 89–98% ee were synthesized in 40–92% yield by a Pd-catalyzed reaction of the respective allylic acetates and carbonates rac- 1a, rac- 1b, rac- 10a, rac- 10b and rac- 14a–c with LiO 2S t-Bu in the presence of the chiral ligands 2a, ent- 2b and 12. Formation of the n-butyl sulfones 13a and 13b of 95% ee was observed. Reactions of rac- 1a and 1b/ ent- 1b with LiO 2S t-Bu in the presence of 2a and ent- 2b, respectively, in THF under heterogeneous conditions were accompanied by a kinetic resolution of the allylic substrates. The faster reacting allylic substrate and the preferentially formed sulfone had the same absolute configuration. The allylic tert-butyl sulfide 17 of 92% ee was obtained in 63% yield by the Pd-catalyzed reaction of rac- 1b with Me 3SiS t-Bu in the presence of ent- 2b.