Five 3,4-dihydro-2H,5H-pyrano[3,2-c][1]benzopyran-5-one derivatives

wThe molecular structures of five 3,4-dihydro-2H,5H-pyrano[3,2-c][1]benzopyran-5-one derivatives, namely, cis,anti-7,7a,8,9-tetrahydro-7-phenyl-6H, 10aH-furo-[2',3':2,3]pyrano[5,6-c][1]benzopyran-6-one [C20H16O4,(I)], cis-2-ethoxy-3,4-dihydro-4-furyl-2H,5H-pyrano [3,2-c][1]benzopyran-5-one [C18H16O5, (II)], cis-2-ethoxy-3,4-dihydro-4-phenyl-2H,5H-pyrano[3,2-c][1]benzopyran-5-one [C20H18O4, (III)], cis-2-ethoxy-3,4-dihydro-4-(2-nitrophenyl)-2H,5H-pyrano[3,2-c][1]benzopyran-5-one [C20H17NO6, (IV)] and methyl cis-2-ethoxy-3,4-dihydro-5-oxo-4-phenyl-2H,5H-pyrano[3,2-c][1]benzopyran-4-carboxylate [C22H20O6, (V)] have been studied by single-crystal diffractometry. The conformation of the dihydropyran ring is compared with that found in 36 entries in the Cambridge Structural Database [version of 28 February 1997; Alien & Kennard (1993). Chem. Des. Autom. News, 8, 31-37]. A scatterplot of the conformation of 46 independent molecules is shown. These molecules present a more or less distorted half-chair conformation, with few exceptions; in particular, it seems that molecules with a second ring fused to the dihydropyran moiety adopt a diplanar conformation.