Mechanism of steroidal enol ether formation. Configuration of tritium at C-6 of estra-1, 3, 5(6)-trien-3-OL-17-one-6,7-3H as established during the synthesis of 19-nor-17α-pregna-3, 5-dien-20-yn-17-OL-7-3H 17-acetate

The nature of the reactions involved in the synthesis of 3-cyclopentyloxy-19-nor-17α-pregna-3, 5-dien-20-yn-17-ol-7-3H 17-acetate, allowed the determination of the stereochemistry of the tritium atoms at C-6 in some of the precursors. One of these precursors was estra-1, 3, 5 (6)-trien-3-ol-17-one-6, 7-3H in which 82% of the tritium was in the 6α position and 18% in the 68 position. Supportive evidence for the mechaniam of enol ether formation was obtained, also. Acid catalysed enol ether formation, stereospecifically removed the triton form the 68 position. On hydrolysis of the enol ether, the proton stereospecifically entered the 68 position. Equilibration with base completed the removal of the tritium from the C-6 position.