An improved synthesis of the 5-deoxy-5-(hydroxyphosphinyl)- d-glucopyranoses, and crystal structures of 1,2,3,4,6-penta-O-acetyl-5-deoxy-5-[(R)-methoxyphosphinyl]- β-d-glucopyranose and its 5-[(R)-ethylphosphinyl] congener

Treatment of 3-O-acetyl-5-deoxy-5-(dimethoxyphosphinyl)-1,2-O-isopropylidene- α-d-glucofuranose (7) with dihydropyran in the presence of pyridinium p-toluenesulfonate gave the 6-O-(tetrahydropyran-2-yl) derivative in 91% yield. Ring-enlargement of this compound by the known, 2-step procedure gave 5-deoxy- 5-(hydroxyphosphinyl)-d-glucopyranoses in an overall yield from 7 twice as high as that obtained by the previous, alternative route via the corresponding 6-O-(triphenylmethyl)- α-d-glucofuranose precursor. X-Ray crystallographic analyses were performed on the two title compounds, penta-O-acetyl-5-deoxy-5-(methoxyphosphinyl)- (12b) and -5-(ethylphosphinyl)-β-d-glucopyranose (13b). The results show that both have the ⁴C₁ conformation and the substituents on C-1 to C-5 are quasi-equatorial (nomenclature of Jeffrey and Yates). The methoxy group of 12b is in a quasi-equatorial position, whereas the ethyl group of 13b is attached bisectionally to P-5.