E. Dane's Route to Estrone Revisited

Article abstract of DOI:10.1016/S0040-4039(00)92705-9

The chirogenic Diels/Alder reactions of the general pattern AB + D -> ABCD (i): 2 + 3 -> rac-8a (major) + rac-9a (minor) (85percent), (ii): 2 + 10a -> rac-11a (89percent) and (iii): 2 + 10b -> rac-11b (90percent), now have been accomplished in the presence of Lewis acid, (i): BF3*Et2O, (ii) or (iii): TiCl4.Case (iii) may be used as the initial move towards (+/-)-norgestrel (rac-14).