Journal of the American Chemical Society p. 5602 - 5612 (1984)
Update date:2022-08-10
Topics:
Zimmerman, Mary P.
Li, Hui-ting
Duax, William L.
Weeks, Charles M.
Djerassi, Carl
By using the unique stereochemistry of the side chain in cholesterol, the dynamic influence of proximate chiral centers on the acid-promoted isomerizations of cyclopropanes is defined.Unexpectedly, when the cyclopropane is placed in the 22,23 position, either a backbone rearramgement is induced or a priori unanticipated side-chain olefins arise, each dependent on the stereochemistry of the cyclopropane starting material.The synthesis and stereochamical assignments of the four possible 22,23-methylenecholesterol acetates <22R,23R (22), 22S,23S (23), 22S,23R (24), 22R,23S (25)> are reported as well as the effect of stereochemistry on the acid-promoted isomerization of these compounds.Isomers 22 and 23 under the conditions of ring opening yield unexpected backbone rearrangement products of the 3β-acetoxy-(17S)-17,23-dimethyl-18-normethylcholest-5,13(14)-diene type (32-35), which can also be obtained from rearrangement of the Δ5,20(22)- and Δ5,17(20)-23-methylcholestadien-3β-ol acetates (42,44,53,54).The stereochemical criteria governing the course of these isomerizations are discussed.
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