Five 3,4-Dihydro-2H,5H-pyrano[3,2-c][1]benzopyran-5-one Derivatives

The 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; Allen & Kennard (1993). Chem. Des. Autom. News, 8, 31-37]. A scatterplot of the conformation of 46 independent molecules is shown. These molecules all 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.

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