Stereochemistry of nitrogenous heterocycles. 71. Isomerization ? Equilibration of stereoisomeric ethinylcarbinols epimeric at the carbinol center

Abstract

Equilibration of stereoisomeric cyclic ethinylcarbinols, epimeric at the carbinol center, was conducted for the first time and it was shown that the equilibrium is shifted toward the equatorial alcohol (at 50‡C for 2e-methyl-4-hydroxy-4-phenylethinyl-trans-decahydroquinoline, 2e-methyl-4-hydroxy-4-ethinyl-trans-decahydroquinoline, 4-hydroxy-4-ethinyl-trans-decahydroquinoline —(78±1)% equatorial and (22±1)% axial alcohol, for 1,2e,5e-trimethyl-4-ethinylpiperidol-4 (74±1)% equatorial and (26±1)% axial alcohol). The epimerization of stereoisomeric ethinylcarbinols can be used as a method for determination of the configuration of the quaternary carbinol center.