Synthesis of cyclocholates and derivatives, III - Cyclocholates with 12-oxo and 7,12-oxo groups

Syntheses of bile acid cyclooligomers with 12- and 7,12-oxo groups (6a-d, 7a-c, 8a-b) by the Yamaguchi method are described. Cyclotrimerization is the principal reaction route for these cholic acid systems. Conversion of 7- and 12-hydroxy groups in cholic acid (1a-b) to oxo groups (4a-c, 5a-c), followed by macrocyclization (6a-d, 7a-c, 8a-b) and selective reduction of the oxo groups back to hydroxy ones without cleaving the 24-carboxylic ester Linkages (11) constitutes a new strategy in the synthesis of cyclocholates having unprotected hydroxy groups.