(1 beta, 5 alpha, 6 beta)-10,10- (1,2-ethylenedioxy)-1,5-dimethylbicyclo[4.4.0]decan-4-one

The title compound (1) [alternative name: 5,8a-dimethyl(decahydronaphthalene)-1-spiro-2'-(1',3'-dioxolan+ ++)-6-one, C14H22O3] was obtained as the major product upon Pd/CaCO3-catalyzed hydrogenation of the corresponding enone (2). The analysis of the crystal structure of (1) has established that the monoacetal is cis-fused and that both rings adopt nearly perfect chair forms. The C(5) methyl group is in an alpha position, resulting directly from syn-hydrogenation of the enone. While there are two possible chair-chair conformations for cis-decalins, the title compound crystallized in the conformation which places the C(5) methyl group in an equatorial position.