Asymmetric synthesis of planar-chiral paracyclophanes by double C-S bond formation: comparison of catalytic activity and enantioselectivity of Pd and Rh catalysts.
英文:
Asymmetric synthesis of planar-chiral paracyclophanes by double C-S bond formation: comparison of catalytic activity and enantioselectivity of Pd and Rh catalysts.
The authors have detd. 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 the previously reported cationic rhodium(I)/(S)-BINAPHANE complex-catalyzed ones, the palladium(II)-catalyzed reactions allowed the use of com. 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. [on SciFinder(R)]
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