Crystal structures of three 1-arylpropane-1,2-diol 2-aryl ether derivatives and the acetate of 2,6-dimethoxy-4-(1-(E)-propenyl)phenol

Abstract

The crystal structures ofthreo-2-[2,6-dimethoxy-4-(1-(Z)-propenyl)phenoxy]-1-(4-hydroxy-3,5-dimethoxyphenyl)-1-propanol (7b),threo-2-(2,6-dimethoxy-4-propylphenoxy)-1-(3,4-5-trimethoxyphenyl)-1-propanol (7c), the diacetate oferythro-2-[2,6-dimethoxy-4-(1-(Z)-propenyl)phenoxy]-1-(4-hydroxy-3,5-dimethoxyphenyl)-1-propanol (8d) and the acetate of 2,6-dimethoxy-4-(1-(E)-propenyl)phenol (9) have been determined by single-crystal X-ray diffraction methods;7b,7c, and8d are structurally closely related to a class of optically-active neolignans of 1-arylpropane-1,2-diol 2-aryl ether type occurring in plant extracts. The reflection intensities were recorded at room temperature for7b and8d, at -140°C for7c and at -120°C for9. Compound7b crystallized as needles in the orthorhombic space groupPna2₁ witha=27.055(3),b=11.850(8),c=6.717(4)Å andZ=4.R became 0.041 for 1792 observed [I>3σ(I)] reflections used in the refinement of the structure. Compound7c crystallized as prisms in the monoclinic space groupP2₁/a witha=12.565(4),b=13.96(1),c=12.846(7)Å,β=93.86(3)° andZ=4. The refinement gaveR=0.051 for 2101 observed [I>3σ(I)], unique reflections. Compound8d crystallized as prisms in the monoclinic space groupP2₁/n witha=13.182(4),b=8.518(5),c=23.322(5)Å,β=106.12(2)° andZ=4. The finalR-valuebecame 0.042 for 2131 observed [I>3σ(I)], unique reflections. Compound9 crystallized as prisms in the orthorhombic space groupPca2₁ witha=18.216(4),b=9.483(3),c=7.416(2)Å andZ=4. TheR-value became 0.038 for 1502 observed [I>3σ(I)], unique reflections. The crystals of7b are stabilized by moderately strong hydrogen bonds. All the 1-arylpropane-1,2-diol 2-aryl ethers examined adopted conformations in which the aromatic groups tend to be as remote as possible. Observed double bond lengths in the propenyl groups of the compounds examined (≈1.30 Å) deviate significantly from the expected value (≈1.34 Å). The cause of this discrepancy is discussed.