Molecular structure of the double Diels–Alder cycloadduct of 2-pyrone and cycloocta-1,5-diene. Very close intramolecular H/H contact and some comments

Abstract

The molecular structure of the double Diels–Alder adduct (DDA) of 5-methoxycarbonyl-2-pyrone and 1,5-cyclooctadiene has been clarified by single crystal X-ray analysis on the phenylurethane of the hydroxymethyl derivative obtained from LiAlH₄ reduction of the DDA adduct. The X-ray analysis indicates that the DDA adduct has very close non-bonded H/H contacts of ca. 1.94 Å. The observed data are compared with those derived from the MM- and MO-optimized structures.