B-homo-19-norsteroids

A promising general method for preparing B-homo-19-norsteroids has been reported by Tadanier and Cole in a study of the horaallylic rearrangements of 19-substituted-A -steroids. The ready availability of 19-hydroxy-A -steroids cf. ehapter 12) makes this approach particularly attractive. 

Acetolysis of 3/ -methoxy-19-hydroxy-androst-5-en-17-one 19-methane-sulfonate (68b) in the presence of 4 equivalents of potassium acetate at 100° for 16 hr followed by basic hydrolysis gives 3/ -methoxy-7) -hydroxy-B-homo-estr-5(10)-en-17-one (70a) in 77% yield and 8% of 3/ -methoxy-5, 19- 

Tadanier also found that the interconversion of (69a), (70a) and (71a) (see Chart I) could be achieved under distinct conditions of solvolysis and suggested a series of equilibrating cations to account for these observations (see Chart II). 

Recent work by Syhora, Edwards and Cross has confirmed the p-orientation of the substituent introduced at C-6 in 5, 19-cyclo steroid (69) in the kinetically controlled hydrolysis of A -19-methanesulfonoxy steroids. 

The nature and stereospecificities observed in the rearrangement of (68b) to (69a) and (69a) to (70a) suggests that these rearrangements involve two discrete carbonium ion intermediates A and B (see Chart II). 

---

A-homo-B-nor-5/3-choIestan-4a-one, 394 A-homo-B-norsteroids, 389 B-homo-19-norsteroids, 379 B-homo-5a-pregnane-3, 20/3-diol diacetate, 376... 

---