Quinolinophane-derived alkyldiphenylphosphines: two homologous P,N-planar chiral ligands for palladium-catalysed allylic alkylation

Two novel homologous [2]paracyclo[2](5,8)quinolinophane-derived P,N-bidentate planar chiral ligands have been synthesised and their effectiveness in asymmetric catalysis tested in palladium-catalysed allylic malonylation of 1,3-diphenylpropenyl acetate. The extent of asymmetric induction depends linearly on the ligand/metal molar ratio, indicating the involvement of P,P-type and chelate P,N-type π-allylpalladium complexes in equilibrium. The length of the chain that binds the diphenylphosphine group to the quinolinophane moiety, while appreciably affecting the P,N-complex stability, has little effect on the extent of asymmetric induction, which is due to the greater reactivity of the [PN]-exo–syn–syn– ([PN]xss) with respect to the [PN]-endo–syn–syn– ([PN]nss) π-allylpalladium complex.

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(R)-2-[(Diphenylphosphino)methyl]-4-methyl[2]paracyclo[2](5,8)quinolinophane borane complexC33H33BNPEe = 100%[α]D20=+6.7 (c 0.67, CH2Cl2)Source of chirality: chiral building blockAbsolute configuration: (Rp)

(R)-2-[(Diphenylphosphino)methyl]-4-methyl[2]paracyclo[2](5,8)quinolinophaneC33H30NPEe = 100%[α]D20=+3.1 (c 4.4, CH2Cl2)Source of chirality: chiral building blockAbsolute configuration: (Rp)

(R)-2-(Bromomethyl)-4-methyl[2]paracyclo[2](5,8)quinolinophaneC21H20BrNEe = 100%[α]D25=-11.5 (c 0.5, CHCl3)Source of chirality: chiral building blockAbsolute configuration: (Rp)

(R)-2-[2-(Diphenylphosphino)ethyl]-4-methyl[2]paracyclo[2](5,8)quinolinophane borane complexC34H35BNPEe = 100%[α]D20=+37 (c 0.48, CHCl3)Source of chirality: chiral building blockAbsolute configuration: (Rp)

(R)-2-[2-(Diphenylphosphino)ethyl]-4-methyl[2]paracyclo[2](5,8)quinolinophaneC34H32NPEe = 100%[α]D29=+17 (c 0.51, CHCl3)Source of chirality: chiral building blockAbsolute configuration: (Rp)