Acyloin rearrangements

Keywords 17a-hydroxy-20-ketosteroid, acyloin rearrangement, substitutive rearrangement, stereoselective, gas-solid reaction... 

A-acyliminium ions (equations 41, 43, 55 and 56) Danilov rearrangement of aldehydes 347 into ketones 349149 (equation 95), the acyloin rearrangement 350 -> 35290 (equation 96) and dienone-phenol rearrangement 353-355150 (equation 97). 

Several examples are known of the contraction of steroid rings by benzilic acid rearrangements of a -diketones [2g2]. Acyloin rearrangements in the steroid field, particularly in the conversion of i7-hydroxypregnan-20 ones into D-homo-ketols,... 

A reaction similar in character to the base-catalysed acyloin rearrangement occurred when the i7a-hydroxy-20-ketone was heated in liquid ammonia [216]. The product, a i i mixture of i7a-epimeric amino-17-ketones (7) and (8) is best explained... 

Nitro derivatives of a tribromophenol homolo t. Zincke and Breitweiser [116] have found that dinitraiion of a tribromophenol homologue in the presence of acetic acid yielded two isomeric products. It was recently established (due to modern methods) (117) that nitration can also produce an interesting acyloin rearrangement leading to a five-member ring compound according to scheme (IS) ... 

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. 

An interesting base-catalysed cyclization of the bromo-diterpenoid sphaerococcenol A (120) to generate the cyclobutane (121) involves an acyloin rearrangement prior to an intramolecular displacement. 

Another reaction which indicated that the CD ring structure of aconitine is similar to that of delphinine was the oxidation of oxonine (CXXXVIII), the hydrolysis product of oxonitine (CXXXIII), with Sarett s reagent to obtain the rearranged diketone CXL. The latter is assumed to arise from a base-catalyzed acyloin rearrangement of the original oxidation product (CXXXIX) which was not isolated. 

The FeCl3-Si02 reagent is also useful for pinacol and acyloin rearrangements. Examples ... 

In contrast, treatment of the bicyclo[2.2.2]octenone bearing a nitro (NO2) group with KHMDS led only to the epimerization of the C-7 stereocenter in the substrate, whereas KH in THF or NaH in DMF induced the acyloin rearrangement in good yields. 

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