Furanosteroid Studies. Stereoselective Synthesis of the A,B,E-Ring Core of Wortmannin

Alkyne oxazole 11c is converted in three steps, and
∼45% overall yield, to furanolactone 21α
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 23α,β (dynamic kinetic resolution).

炔基恶唑11c经三步反应，以约45%的总收率转化为呋喃内酯21α，该产物拥有渥曼青霉素（wortmannin）家族呋喃甾类化合物的A、B、E环核心结构。四氯化钛(TiCl₄)催化乙氧羰基甲醛(EtO₂C−CH=O)对呋喃酸14d中C3与C10位的插入反应，通过涉及平衡态羟醛中间体23α,β的化学选择性内酯化路径，实现了大于98%的立体选择性，该过程属于动态动力学拆分。