Corona-Díaz, A., García-Merinos, J.P., Ochoa, M.E., del Río, R.E., Santillan, R., Rojas-Lima, S., Morzycki, J.W., López, Y., TiCl4 catalyzed cleavage of (25R)-22-oxo-23-spiroketals. Synthesis of sapogenins with furostanol and pyranone E rings on the side chain. Steroids, 152 (2019) 108488, DOI: 10.1016/j.steroids.2019.108488
The regioselective opening of the F ring of 22-oxo-23-spiroketals 7a-d using TiCl4 in acetic anhydride yielded the novel furostanols 11a-d along with cholestanic derivatives 8a-d with pyranone E ring. The structures of the new derivatives thus obtained were established using one- (DEPT) and two-dimensional 1H, 13C NMR experiments (COSY, HSQC, HMBC, NOESY). The 22?-hydroxyl orientation in compounds 11a-d was proposed by comparison of the 13C chemical shifts with those of other aglycone members of this family, and confirmed by combined NOESY and X-ray diffraction analysis of compound 11a.