THE CRYSTAL-STRUCTURE OF METHYL 4,6-O-BENZYLIDENE-2,3-O-DIBUTYLSTANNYLENE-ALPHA-D-GLUCOPYRANOSIDE

The determination of the crystal structure of methyl 4,6-O-benzylidene-2,3-O-dibutylstannylene-alpha-D-glucopyranoside (1) was repeated from data collected at -70-degrees-C because the previous assignment had a large R value (10.9%) and because this structure was the key link in assignment of structures of all stannylene acetals in solution. Crystals of 1 are orthorhombic, of space group P2(1)2(1)2(1), with a = 12.479(2), b = 19.202(5), c = 19.654(6) angstrom, Z = 4, R = 0.0597 (R(w) = 0.0612) for 3623 independent reflections with I > 3sigma(I). Compound 1 is a dimer linked together by a four-membered 1,3-dioxa-2,4-distannetane ring containing the O-3 atoms from the two glucose units. Deviations from C2 symmetry are much smaller than reported earlier and lie mainly in the orientations of the butyl groups. The butyl groups are still significantly disordered at -70-degrees-C. It is suggested that steric effects of these flexible butyl groups may be an important factor in the selectivity for dicoordinate oxygens previously observed in reactions of stannylene acetal dimers with electrophiles.