Stereochmical Effects in Cyclopropane Ring Openings: Synthesis and Isomerization of Petrosterol and All Three of Its Trans Cyclopropane Diastereomers

Article abstract of DOI:10.1021/ja00331a035

All four trans isomers of the marine sterol petrosterol, with a side chain terminating in a cyclopropane ring, have been synthesized.The absolute stereochemistry of the diastereomers was determined by correlation with compounds of known absolute stereochemistry.The product distribution resulting from the acid-catalyzed isomerization of these four diastereomers shows a marked dependence on the relative stereochemistry between the cyclopropane ring and the adjacent chiral center at C24.A careful examination of the conformations available to the side chain leads to a rational explanation of this dependence, and sheds light on hitherto unrecognized subtle stereochemical features operating among aliphatic cyclopropanes.In addition we report the synthesis and acid-catalyzed ring opening of (24S,25S,26S)-22,22-dideuteriopetrosterol and the confirmation by this labeling study that one of the products of the isomerization reaction arises via a 1,5-hydride-shift mechanism.