Tailor-made chiral pyranopyrans based on glucose and galactose and studies on self-assembly of some crystals and low molecular weight organogel (LMOG)

摘要

InCl_3 catalyzed reactions of 2-C-acetoxymethylglycal derivatives with different phenolic compounds resulted in the formation of sugar based pyranoarenopyrans in good yields and moderate to excellent diastereoselectivity in favor of 10aR- or 12aR- or 14aR-products. One of the synthesized compounds, viz. (2R,3R,12aR)-2,3,5,12a-tetrahydro-2-methoxymethyl-3-methoxypyrano[2,3-b] naphtho[1,2-e]pyran gelated polar solvents like MeOH, EtOH and non-polar solvents like pentane, hexane, heptane, octane, pet. ether, etc. The SEM picture of the corresponding hexane xerogel exhibited a rare type of microtubular gel assembly, whereas the SEM pictures of MeOH and pet. ether xerogels showed different types of three-dimensional network. Study of the MeOH gel by Fluorescence spectroscopy, ~1H NMR and X-ray powder diffraction analysis indicated that the supramolecular assembly in the MeOH gel can be attributed to π-stacking. The crystal packing of (2R,3R,10aR)-3,10a-dihydro- 2-methoxymethyl-3-methoxy-7-methyl-2H,5H-pyrano[2,3-b][1]benzopyran, a benzopyran analogue of the above organogelator was stabilized by C-H?O and C-H?π hydrogen bonds forming one-dimensional columns parallel to the [001] direction, whereas the corresponding benzopyran 3-epimer showed only C-H?O hydrogen bonds among the molecules.