Issue 17, 2001

Diphosphines based on an inherently chiral calix[4]arene scaffold: synthesis and use in enantioselective catalysis

Abstract

A series of calix[4]arenes bearing two phosphorus pendent groups p-But-calix[4]arene-25,26-[CH2P(O)Ph2]2-27-(OR1)-28-(OR2) (R1 or 2 = CH2CO2Et, R2 or 1 = H, 2; R1 = R2 = CH2CO2Et, 3; R1 or 2 = C(O)Ocholesteryl, R2 or 1 = H, 4; R1 = R2 = C(O)Ocholesteryl, 5; R1 or 2 = (R)-CH2C(O)NHCMe(Ph)H, R2 or 1 = H, 6) and p-But-calix[4]arene-25,26-(CH2PPh2)2-27-(OR1)-28-(OR2) (R1 = (R)-CH2C(O)NHCMe(Ph) H, R2 = H, 7; R1 = (R)-CH2C(O)NHCMe(Ph)H, R2 = SiMe3, 8; R1 = (R)-CH2C(O)NHCMe(Ph)H, R2 = (R)-CH2C(O)NHCMe(Ph)H, 10) have been synthesised. The enantiomerically pure calixarenes 7, 8 and 10 having an AABC substitution pattern are inherently chiral. Reaction of the latter three diphosphines with [Pd(2-Me-allyl)(THF)2]BF4 (THF = tetrahydrofuran) afforded the chelate complexes [Pd(2-Me-allyl)(diphosphine)]BF411–13, respectively, while reaction with [Rh(NBD)(THF)2]BF4 (NBD = norbornadiene) resulted in quantitative formation of the complexes [Rh(NBD)(diphosphine)]BF414–16, respectively. As a result of allyl rotation, the palladium complexes 11–13 exist in solution as two interconverting species. These complexes efficiently catalyse the alkylation of 1,3-diphenylprop-2-enyl acetate with dimethyl malonate, the turnovers being ca. 30 h−1. Enantioselectivity was shown to depend on the size difference between the B and C substituents. Thus, while virtually no induction was observed with the chiral calixarene 10 bearing two identical substituents, ee’s of 45% and 67% respectively were observed with 12 and 11, which have a more marked dissymmetry. Similar trends were observed in the catalytic hydrogenation of dimethyl itaconate with the rhodium complexes 14–16, leading to ee’s of 48%, 25% and 0%, respectively. Related chiral calixarenes in which the two phosphine arms occupy proximal instead of distal phenolic positions were found to be considerably less effective in catalysis of both allylic alkylation and hydrogenation.

Graphical abstract: Diphosphines based on an inherently chiral calix[4]arene scaffold: synthesis and use in enantioselective catalysis

Supplementary files

Article information

Article type
Paper
Submitted
12 Feb 2001
Accepted
12 Jun 2001
First published
08 Aug 2001

J. Chem. Soc., Dalton Trans., 2001, 2508-2517

Diphosphines based on an inherently chiral calix[4]arene scaffold: synthesis and use in enantioselective catalysis

C. Dieleman, S. Steyer, C. Jeunesse and D. Matt, J. Chem. Soc., Dalton Trans., 2001, 2508 DOI: 10.1039/B101369F

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