STEREOCHEMISTRY OF CYCLIC-COMPOUNDS .1. SYNTHESIS AND CONFIGURATIONAL ASSIGNMENT OF DIASTEREOMERIC 2,4-DIOXASPIRO[5.5]UNDEC-8-ENES

Several 2,4 - dioxaspiro[5.5]undec - 8 - enes have been prepared from the Diels-Alder adducts of butadiene and 2,3-dimethylbutadiene with acrolein. Contrary to literature reports on some 3-substituted derivatives, which were assumed to be pure compounds, it is shown that these spiro compounds are generally obtained as 1:1 mixtures of two diastereomers. The isomers have been separated in the case of the 3-methyl and 3-ethyl derivatives by fractional distillation. On the basis of 1H NMR spectroscopy, the nature of the isomerism is shown to be of cis, trans type and an unambiguous cofigurational assignment of the isomers has been achieved. Although the diastereomers are of similar topography, they have distinctly different olfactory properties. © 1979.