The crystal data for p-nitrobenzylidene-p-dimethylaminoaniline (I) are: monoclinic, space group P21/c; a= 11.065 (2), b=7.759 (2), c= 16.488 (2)/~,, fl= 106"53 (3) °, Z=4. The crystal data for p-dimethylaminobenzylidene-p-nitroaniline (II) are: triclinic, space group P]'; a=9.509 (1), b= 16.200 (1), c= 9-505 (1) ~, e=91.69 (1), fl= 107.52 (1), 9,= 101"04 (1) °, Z=4 (two independent molecules in the asymmetric unit). The intensity data were collected on a four-circle diffractometer using Zr-filtered Mo Ke radiation. The structures were refined by a block-diagonal least-squares method to R indices of 0.081 for (I) and 0.070 for (II). The molecule (I), as a whole, is in a nearly planar conformation, and (II) in a non-planar one. The twist angles of the aniline ring out of the C-N=C-C plane are 9.2 ° for (I), and 41.5 and 49.0 ° for (II). The twist angles of the benzylidene ring range from 4.1 to 11"4 °.

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The crystal structures of 3-methyl-4-nitropyridine N-oxide (M4NPO), tetragonal 3,5-dimethyl-4-nitropyridine N-oxide (D4NPO-T) and orthorhombic D4NPO (D4NPO-O) have been determined. M4NPO is ortho-

Interglycosidic spiro ortho esters (9-20) were efficiently prepared from methyl 2,6-di-O-benzylgluco- or galactopyranoside and various sugar lactones in the presence of methoxytrimethylsilane and a catalytic amount of trimethylsilyl triflate. All of the prepared sugar ortho esters possess perhydrospiro[2H-pyran-2,2'-pyrano[3,2-d][1,3]dioxin] ring systems commonly in their molecules and, remarkably, were afforded as single isomers. The configurations of the spiro centers in their molecules were determined or estimated by X-ray single crystallographic analysis and molecular modeling studies. By comparing the conformations of prepared ortho esters, we revealed that the difference in the stability between two possible isomers was principally caused from that between the spiro ring systems in their molecules in each case.