Asymmetric synthesis of planar-chiral paracyclophanes by double C–S bond formation: comparison of catalytic activity and enantioselectivity of Pd and Rh catalysts

We have determined that a cationic palladium(II)/(R)-BINAP complex is able to catalyze enantioselective double C–S bond-forming reactions between dithiols and dibenzyl dibromides leading to planar-chiral dithiaparacyclophanes. Although the yields and ee values of the palladium(II)-catalyzed syntheses of dithiaparacyclophanes did not exceed our previously reported cationic rhodium(I)/(S)-BINAPHANE complex-catalyzed ones, the palladium(II)-catalyzed reactions allowed the use of commercially available and inexpensive (R)-BINAP as a ligand. On the other hand, an almost racemic product was obtained by using a cationic rhodium(I)/(R)-BINAP complex as a catalyst.

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(−)-12,15-Dimethyl-2,9-dithia[10]paracyclophaneC16H24S2[α]D25=-3.7 (c 1.88, CHCl3)Ee = 8%Source of chirality: [Pd(CH3CN)4](BF4)2/(R)-BINAP