Stereoisomerism in the Cycloadducts from 4-Alkyl-1-vinylcyclohexenes with Maleic Anhydride, Sulfur Dioxide, and Methylphosphonous Dichloride

Article abstract of DOI:10.1021/jo00138a009

Cycloaddition of 4-methyl-1-vinylcyclohexene with the dienophiles of the title gave adducts which consisted of a mixture of diastereoisomeres.The 13C NMR spectra of the mixtures revealed the isomerism to arise from equatorial (syn isomer) or axial (anti isomer) disposition of the methyl group relative to the newly created chiral carbon of the cyclohexane ring.In every case, the predominating isomer was that with an axial methyl.Such isomers also were formed when these dienophiles were reacted with 4-tert-butyl-1-vinylcyclohexene.In some cycloadditions conducted overprolonged reaction periods, changes in the isomer ratio occurred, and the favored product became the thermodynamically more stable syn form.In the cycloaddition with CH3PCl2, some rearrangement of the double bond in the cycloadduct to the ring-fusion position occurred.All of the six possible isomers (hexahydrophosphindole derivatives) were formed on hydrolysis of the adduct mixtures.