Enantiomerically pure Diels-Alder adducts of maleic anhydride to furfural acetals through thermodynamic control. Single crystal and molecular structure of (1S,4R,4'S,5'S)-1-(4',5'-dimethyldioxolan-2'-yl)-5,6-dimethylidene-7-oxabicyclo[2.2.1]hept-2-ene

The acetal of (2S;,3S)-butane-2,3-diol and furfural is equilibrated in molten maleic anhydride with one major crystalline product which is a 1:1 complex of maleic anhydride and (1S,2R,3S,4R,4'S,5'S)-1-(4',5'-dimethyldioxolan-2'-yl)-7-oxabicyclo [2.2.1]hept-5-ene-2-exo,3-exo-dicarboxylic anhydride. This compound was converted into (1S,4R,4'S,5'S)-1-(4',5'-dimethyldioxolan-2'-yl)-5,6-dimethylidene-7-oxabicyclo[2.2.1]hept-2-ene (+)-12, the circular dichroism spectrum of which suggests a slightly skew s-cis-butadiene chromophore as confirmed by X-ray diffraction. Copyright (C) 1996 Elsevier Science Ltd