D-Homo rearrangement

If the final product is prone to D-homo rearrangement during the hydrolysis step, cleavage of the oxalolactone with ethylenediamine instead of inorganic base avoids this complication. ... 

Since 17a-ethynyl-17 -hydroxy steroids are so readily prepared, they represent attractive starting materials for conversion to 20-ketopregnanes. Standard methods for the hydration of aliphatic acetylenes (e.g, mercuric salts alone, with aniline, or with BF3) give variable results, and sometimes no product at all, due to D-homo rearrangement. 233,235,265-7 mercury... 

The C-nor-D-homo rearrangement has been effected by methods other than i2j sulphonate solvolysis, including the deamination of a i2jS-amine (7) [iii] and the decomposition of i2-toluene- sulphonylhydrazones (8) under basic conditions [io8,iog,ii2]. It is both convenient and instructive to consider these reactions together, especially since the com-... 

C-nor-D-homo rearrangement of a I4 hydroxy-i2) -tosyloxy steroid y. Shimizu and H. Mitsuhashi, Tetrahedron, 24 (1968) 4207. 

D-homo rearrangement of steroids. Originally discovered in 17 (i - h ydro x y -20 -ke to stero id s, but thoroughly studied in the 17a-hydroxy-20-keto series, this reaction involves an acid- or base-catalyzed acyloin rearrangement that yields a 6-mem-bered D-ring. 

These results indicated that the Wagner-Meerwein-type rearrangement was followed by a stereospecific hydride transfer from C-18a to C-13a which led to an immonium ion, the latter finally being reduced to derivative (11) (Scheme 1). Inversion at position 12, as expected for a Wagner-Meerwein-type rearrangement, is in accordance with the generality of the c-nor-D-homo rearrangement. 

By the action of collidine, a successful c-nor-D-homo rearrangement of lip-mesyloxy-NJV -dicyanodihydroconimine (16a) in a non-reductive medium has been reported to give a mixture of two ethylenic main products. These have been shown to have tetrasubstituted double bonds and their possible structures are (17), (18), or (19). The presence of the derivatives (17) and (18) in the reaction... 

The D-homo rearrangement reported for 17a-hydroxy-20-keto steroids is adequately described by Wendler. Possible products of this rearrangement are shown below. 

While not specifically described in the literature, the D-homo rearrangement may be a possible occurrence for dexa-methasone under certain reaction conditions by analogy with other steroids such as triamcinolone. ... 

Other references related to the D-homo rearrangement are cited in the literature. ... 

Certain olefins of steroids were prepared in good yield by reducing the enol diethylphosphates of a-bromoketones with lithium and ammonia in t-butyl olcohol. HMPT and sodium azide act uniquely on certain C 20 tosylates that might normally give D-homo rearrangement to provide azides. 

---