11-Nitrites, photolysis

A unique method for the degradation of 17-hydroxy-20-oxygenated pregnanes to 17-ketoandrostanes involves the photolysis of the corresponding nitrite esters.While this generally is equivalent to bismuthate or periodate oxidations, it is the only mild method for the conversion of a 17-hydroxy- 

20-keto-21-desoxy steroid to the 17-ketone. The following mechanism has been suggested  

However, this does not explain the structural requirements for the oxygen function vicinal to the nitrite ester a-ketones, ketals and hydroxyls are cleaved, but a-acetoxyls are not. 

Androst-4-ene-3,17-dione 17a-Hydroxyprogesterone (1 g) is dissolved in 10 ml of pyridine and treated dropwise at —20° with a solution of nitrosyl chloride in pyridine until a permanent blue color develops. The reaction is quenched with 500 ml of ice water, and the resulting nitrite is filtered and 

A recent communication described the cleavage of 17a-hydroperoxy-20-keto steroids with base to give 17-ketoandrostanes in good yield. Since such hydroperoxides are now accessible from 20-ketopregnanes in one step vide infra), this constitutes a convenient two-step degradation process. In practice, the intermediate hydroperoxide need not be isolated. Other enolizable 

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In most cases the carbon radical formed in the hydrogen abstraction step 2 will react with the radical R formed in the homolysis of the X—R bond. However, a cage reaction does not seem to be involved in this step. This has been established in the nitrite photolysis and probably applies to hypohalites as well. In the lead tetraacetate reaction, the steps following the oxyradical formation leading to tetrahydrofuran derivatives are less clear. 

The conversion of 3y5-acetoxy-5a-bromo-6y5-hydroxyandrostan-17-one to 19-norandrost-4-ene-3,17-dione via nitrite photolysis, nitrosation and oxidation to the 6)5,19-lactone results in an overall yield of about 8%, but clearly optimal yields have not been achieved. 

Nitriles from 19-nitroso-dimers, 270 Nitrite photolysis, 239 19-Nitroso-5a-pregnane-3/8,6/3,20/3-triol... 

Derivatives of 9-nitroanthracens 115 undergo the nitro-nitrite rearrangement from their triplet n, r state to 9-anthrol derivatives 118 as shown66 in equation 57 nitrite photolysis is well known and ESR spectra for the anthryloxy radical 117 can be recorded at room temperature. 

Barton, D. H. R. Beaton, J. M. Geller, L. E. Pechet, M. M. J. Am. Chem. Soc. 1960, 82, 2640. In 1960, Derek Barton took a vacation in Cambridge, Massachusetts he worked in a small research institute called the Research Institute for Medicine and Chemistry. In order to make the adrenocortical hormone aldosterol. Barton invented the Barton nitrite photolysis by simply writing down on a piece of paper what he thought would be an ideal process. His skilled collaborator. Dr. John Beaton, was able to reduce it to practice. They were able to make 40 to 50 g of aldosterol at a time when the total world supply was only about 10 mg. Barton considered it his most satisfying piece of work. 

Atkinson, R W. P. L. Carter, A. M. Winer, and J. N. Pitts, Jr., An Experimental Protocol for the Determination of OH Radical Rate Constants with Organics Using Methyl Nitrite Photolysis as an OH Radical Source, J. Air Pollut. Control Assoc., 31, 1090-1092 (1981). 

To explain the high chemical yield in the transformation A - D, coupled with the fact that the quantum yield for the photodecomposition of nitrites is less than unity, it was suggested that the Barton reaction might take place through a radical "cage mechanism.2 However, recent studies at the Institute on the mechanism of nitrite photolysis have shown this not to be so. Photolysis of an equimolecular mixture of 3/3-acetoxy-androstan-6/8-yl nitrite (102) and 3/8-acetoxy-cholestan-6/8-yf nitrite containing 98% of nitrogen as N16 (103) in iso-octane or toluene... 

Barton Reaction (Barton Nitrite Photolysis Reaction)... 

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