First Steroidal Carbamoyloxa-Bridged Cyclophanes: Regioselective Macrocyclization of Methyl Cholate by Double Transesterification

Shin Irie; Makoto Yamamoto; Keiki Kishikawa; Shigeo Kohmoto; Kazutoshi Yamada

doi:10.1055/s-1996-4343

Synthesis 1996; 1996(9): 1135-1138
DOI: 10.1055/s-1996-4343

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First Steroidal Carbamoyloxa-Bridged Cyclophanes: Regioselective Macrocyclization of Methyl Cholate by Double Transesterification

Shin Irie, Makoto Yamamoto^* , Keiki Kishikawa, Shigeo Kohmoto, Kazutoshi Yamada

^*Department of Materials Science, Faculty of Engineering, Chiba University, 263, Japan, Fax +81(43)2903039

Abstract

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Facile regioselective macrocyclization of methyl cholate (1) using dimethyl α,α,α’,α’-tetramethyl-m-xylylenedicarbamate (2) by transesterification was achieved, in refluxing toluene (0.004 M), using 3% of SnCl₂ and 1% of glycoluril as an additive. After a reaction time of 2 hours, the kinetically favorable 3 was obtained selectively in excellent yield (94%). Conversion of the 16-membered 3 to the 18-membered cyclophane 4 was achieved by establishing an equilibrium (7 days), to give the thermodynamically stable 4 in practical yield (68%). This mild conversion of the regiochemistry of the steroidal macrocycles is remarkable as a characteristic of the carbamoyloxa-bridged cyclophanes. The new steroidal carbamoyloxa-bridged cyclophanes is the first example of a pair of the regioisomeric steroidal cyclophanes.

cholic acid - cyclophane - macrocyclization - carbamate - ring transformation

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