Chiral diphosphites derived from (1R,2R)-trans-1,2-cyclohexanediol: a new class of ligands for asymmetric hydrogenations

A series of novel chiral diphosphite ligands was easily prepared in a few steps from commercial (1R,2R)-trans-1,2-cyclohexanediol as the chiral source, and successfully employed in the Rh-catalyzed asymmetric hydrogenation of α,β-unsaturated carboxylic acid derivatives and enamides with up to 99% ee for dimethyl itaconate and enamides and with up to 94% ee for α-dehydroamino acid esters. The stereochemically matched combination of (1R,2R)-trans-1,2-cyclohexanediol backbone and (S)-binaphthyl in the ligand (1R,2R)-bis[(S)-1,1′-binaphthyl-2,2′-diyl]phosphitecyclohexanediol, was essential for inducing high enantioselectivity. Moreover, the sense of enantiodiscrimination of the products was mainly determined by the configuration of the binaphthyl moieties.

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(1R,2R)-Bis[(R)-1,1′-binaphthyl-2,2′-diyl]phosphitecyclohexanediolC46H34O6P2[α]D25 = −499 (c 0.15, CH2Cl2)Source of chirality: (1R,2R)-trans-1,2-cyclohexanediol and BINOLAbsolute configuration: (1R,2R,Ra,Ra)

(1R,2R)-Bis[(S)-1,1′-binaphthyl-2,2′-diyl]phosphitecyclohexanediolC46H34O6P2[α]D25 = +180 (c 0.18, CH2Cl2)Source of chirality: (1R,2R)-trans-1,2-cyclohexanediol and BINOLAbsolute configuration: (1R,2R,Sa,Sa)

(1R,2R)-Bis[(R)-1,1′-H8-binaphthyl-2,2′-diyl]phosphitecyclohexanediolC46H50O6P2[α]D25 = −153 (c 0.11, CH2Cl2)Source of chirality: (1R,2R)-trans-1,2-cyclohexanediol and H8-BINOLAbsolute configuration: (1R,2R,Ra,Ra)

(1R,2R)-Bis[(S)-1,1′-H8-binaphthyl-2,2′-diyl]phosphitecyclohexanediolC46H50O6P2[α]D25 = +170 (c 0.10, CH2Cl2)Source of chirality: (1R,2R)-trans-1,2-cyclohexanediol and H8-BINOLAbsolute configuration: (1R,2R,Sa,Sa)