X-RAY AND CONFORMATIONAL INVESTIGATION OF ISOMERIC METHYL 2,6-ANHYDRO-3-DEOXY-HEPT-2-ENOATES

The structures of the title compounds of the D-lyxo (1) and D-arabino (2) configurations have been investigated by X-ray methods. The crysta ls of 1 are orthorhombic, space group P2(1)2(1)2(1), and of 2 belong t o monoclinic space group P2(1). The unit cell dimensions are: for 1 a = 8.1789(5), b = 12.2672(7), c = 16.3720(9) Angstrom, and for 2 a = 9. 0749(7), b = 6.5655(5), c = 16.3131(8) Angstrom, beta = 103.58(1)degre es. Both structures were solved by direct methods, and refined by a fu ll-matrix, least-squares procedure. The pyranose ring of 1 and 2 adopt ed H-4(5) conformation slightly deviated in the second compound. Relat ively strong intermolecular hydrogen bonds were observed in the crysta l lattice of 2.