Pregnenolone oxime reaction with

The scheme required to prepare the potent tri-fluoro corticoid cormethasone acetate (292) illustrates the synthetic complexities involved in some of this work. Sequential acetylation of the pregnenolone derivative 278 with first acetic anhydride in pyridine and then acetic anhydride in the presence of tosic acid affords diacetate 279. Reaction of that intermediate with nitrosyl fluoride results initially in addition of the reagent to the 5,6-olefin moiety to afford the fluoro oxime reaction with a second mole of reagent at nitrogen gives the nitroimine derivative 280 passage over alumina serves to hydrolyze the imine function to the corresponding 6-ketone (281). 

The contradictory observations that 16-dehydropregnenolone oxime fails to rearrange with phosphorus oxychloride while pregnenolone oxime undergoes the normal reaction " remain unexplained. The respective 3-acetates in both series rearrange in the expected fashion. 

In an efficient degradation of pregnenolone acetate (8) to androstenolone (14), the first step" consists in reaction of the oxime (9) with phosphoryl chloride in... 

Under these conditions, the initial ketoxime reacts with acetylene quantitatively to deliver O-vinyl oxime (10%), N-vinylpyrrole (63%), and vinyl ethers of pregnenolone as a mixture of epimers (in 25% total yield). The expected migration of the endocyclic double bond or change in the initial configuration of the steroid function is not observed. The major product, doubly vinylated pyrrole-steroid ensemble, contains steroid, vinyl ether, and N-vinylpyrrole fragments in a one molecule, which ensures that different types of chemical modifications are possible including addition and polymerization reactions. 

---