Furanosteroid studies. Stereoselective synthesis of the A,B,E-ring core of wortmannin.

Alkyne oxazole 11c is converted in three steps, and approximately 45% overall yield, to furanolactone 21alpha having the A,B,E-ring core of the wortmannin (2) family of furanosteroids. The TiCl4-catalyzed insertion of EtO2C-CH=O between C3 and C10 in furanoacid 14d is >98% stereoselective via a pathway involving chemoselective lactonization of equilibrating aldol intermediates 23alpha,beta (dynamic kinetic resolution).