Diosphenols

Diosphenol [490-03-9] the main constituent of buchu leaves, is an example of a naturally occurring compound with tautomeric properties (286) ... 

In practice, the scope of the benzilic rearrangement as a tool for the ring contraction of steroids is defined by the availability of a-diketones, or the corresponding diosphenols. 

Several routes to 2,3-diketones have been reported. The most practical and general method is that of Ruzicka, Plattner and Furrer as adapted by Nace and Nelander for synthesis of the diosphenol corresponding to 5a-pregnane-2,3,20-trione (44) starting from 5a-pregnane-3,20-dione (40). The overall yield of diosphenol (44) by this route is 62% based on... 

Benzilic rearrangement of diosphenol (44) gives the A-norsteroid (45) in 90 % yield. 

Hydroxy-5a-pregn-l-ene-3,20-dione (44). To a solution of 7.7 g (15.6 mmoles) of the nitrone (43) in 300 ml of benzene is added 500 ml of 2 A hydrochloric acid, whereupon the deep-red benzene solution immediately turns green. The resulting mixture is stirred for 12 hr and the layers are then separated. The aqueous layer is extracted with three 300-ml portions of benzene the combined benzene layers are washed with 2 N hydrochloric acid and with water, and then dried over sodium sulfate. The benzene is evaporated under reduced pressure to give 4.8 g (93 %) of the diosphenol (44). 

Kubota and co-workers describe a novel oxidative rearrangement of the diosphenol (58) of 17iS-hydroxyandrost-4-ene-2,3-dione to the A-nor-A -1,2-diketone (59) in 33 % yield by the action of specially prep d manganese dioxide in boiling acetone. The rate of ring contraction is very sensitive to the source of the oxidant, and a trace of dilute sulfuric acid in the reaction mixture causes oxidative fission of ring A. 

Diosphenol (58) is easily prepared in 47 % yield from testosterone (60) by acetoxylation with lead tetraacetate followed by oxygenation in an alkaline medium. 

Kubota and co-workers also prepared several 1,2-diols (61) and noted that these substances give the enediones (59) in much better yields than the diosphenols (58). This is consistent with a mechanism which requires, as the first step, hydroxylation of the -double bond of (58) by manganese dioxide followed by oxidation to the intermediate trione. 

A-norsteroids (59) of the cholestane, androstane, pregnane and hydrocortisone series have been prepared from the diols (61)." However, preparation of these 1,2-diols is complicated by concomitant formation of isomeric 4,5-diols, which are usually difficult to separate. The sequence (58) -> (59) appears to be the most practical route to A-norsteroids (59), provided that diosphenol (58) is readily available. 

It has bsen prepared artificially by Semmler and McKenzie by oxidation of oxymethylene-menthone, CjjHjgO, a diketone, CjgHjgOg, resulting, which is inverted by means of alkalis to diosphenol. 

Arihara, S. Riiedi, P. Eugster, C. H. Diterpenoide Driisenfarbstoffe Coleone S und Taus Plectranthus caninus Roth (Labiatae), ein neues Diosphenol/traMS-A/B-6,7-Diketon-Paar aus der Abietanreihe. Helv. Chim. Acta 1977, 60, 1443-1447. 

Ring A diosterols.3 The ring A diosterols (3 and 4) of triterpenes can be prepared from the A2-alkene (1) by osmylation to form the two possible cis-diols (2), which on Swern oxidation give the a-diketone (3). The same diketone is also obtained by Swern oxidation of the 2(3,3a-diol, the product of peracid oxidation followed by acid cleavage. The diketone 3 rearranges to the more stable diosphenol (4) in the presence of base. 

In ethanol 2,4-dinitro-5o -cholestan-3-one, 261, exists entirely as the enol, which is irradiated to give a mixture of diosphenols, 262, and its isomer, 263, in 55% yield (equation 117)136. Similarly, photolysis of an equilibrium mixture of 264 and 265 gives 266 in 48% yield (equation 118). 

The resulting oil was chromatographed on silica gel. Elution with hexane/ether (3 1) gave diosphenol (15 mg, 0.09 mmol), 6-hydroxy-3-methyl-6-isopropylcyclohexane-1,2-dione (3.7 mg, 0.02 mmol) and 2-hydroxy menthone (1.1 mg, 0.006 mmol). All the products were analysed by IR, HNMR and GC-MS. 

Simple polyket. didemnenones Trididemnum cf. cyanophorum, Didemnidae, Ascid. from Bahama Lindquist 1988) diosphenols Ulosa sp., Halichon., Porif. Wratten 1978). 

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