A chiral phosphepine–olefin rhodium complex as an efficient catalyst for the asymmetric conjugate addition

A monophosphine–olefin was synthesised from a 2,2′-bridged 1,1′-binaphthyl precursor, which served as a chiral bidentate ligand in the Rh catalysed 1,4-additions of arylboronic acids to cycloalkenones and 5,6-dihydro-2H-pyran-2-one. Fair yields (64–88%) and high asymmetric inductions (88–98% ee) have been obtained. The crystal structure of a corresponding cationic Rh(I) complex was determined.

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(Sa)-4-Phenyl-4,5-dihydro-3H-dinaphtho[2,1-c;1′,2′-e]phosphepine borane complexC28H24PBEe = 100%[α]D20=+106 (c 1.0, CHCl3)Source of chirality: diastereoselective synthesisAbsolute configuration: (Sa)

(S,Sa,SP)-3-Cinnamyl-4-phenyl-4,5-dihydro-3H-dinaphtho[2,1-c;1′,2′-e]phosphepine borane complexC37H32PBEe = 100%[α]D20=+404 (c 0.5, CHCl3)Source of chirality: diastereoselective synthesisAbsolute configuration: (S,Sa,SP)

(S,Sa,SP)-3-Cinnamyl-4-phenyl-4,5-dihydro-3H-dinaphtho[2,1-c;1′,2′-e]phosphepineC37H29PEe = 100%[α]D20=+286 (c 0.5, CHCl3)Source of chirality: diastereoselective synthesisAbsolute configuration: (S,Sa,SP)