[eta]⁶-Tricarbonylchromium Complexes of Methyl 4,6-O-Benzylidene-[alpha]-D-glucopyranosides

The structures of the [eta]⁶-tricarbonylchromium complexes of four methyl 4,6-O-benzylidene-[alpha]-glucopyranosides, (2)-(5), have been determined, as well as that of the free monosaccharide, (1). These compounds are (R)-methyl 2,3-di-O-methyl-4,6-O-benzylidene-[alpha]-D-glucopyranoside [(1), C₁₆H₂₂O₆], tricarbonyl{(R)-methyl 2,3-di-O-methyl-4,6-O-([eta]⁶-benzylidene)- [alpha]-D-glucopyranoside}chromium(0) {(2), [Cr(C₁₆H₂₂O₆)(CO)₃]}, tricarbonyl{(R)-methyl 2,3-di-O-methyl-4,6-O-[(1R,2S)-2-methylthio-[eta]⁶- phenylmethylene]-[alpha]-D-glucopyranoside}chromium(0) {(3), [Cr(C₁₇H₂₄O₆S)(CO)₃]}, tricarbonyl{(R)-methyl 2,3-di-O-methyl-4,6-O-[(1R,2S)-2-diphenylphosphino-[eta]⁶-phenylmethylene]-[alpha]-D-glucopyranoside}chromium(0) dichloromethane solvate {(4), [Cr(C₂₈H₃₁O₆P)(CO)₃].CH₂Cl₂} and tricarbonyl[(R)-methyl 2,3-di-O-methyl-4,6-O-(4-methoxy-[eta]⁶-phenylmethylene)-[alpha]-D-glucopyranoside]chromium(0) {(5), [Cr(C₁₇H₂₄O₇)(CO)₃]}. These structural studies were undertaken to establish the solid-state conformation of the complexed arene ring in the 4,6-O-benzylidene and the 4,6-O-p-methoxyphenylmethylene [eta]⁶-Cr(CO)₃ complexes, and also the absolute stereochemistry of some ortho-substituted derivatives of the 4,6-O-benzylidene complex.

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