Diazirine ring ketones

The photolysis of cyclic diazo ketones in hydroxylic solvents leads to ring contracted carboxylic acid derivatives via this ketocarbene -> ketene rearrangement. Examples of such reactions are given in (2.24)239) and (2.25) 240). In this last example a photoequilibrium between the diazo ketone and its valence isomer, a diazirine, has been observed, both products then eliminating nitrogen to afford the cyclobutane carboxylic acid. 

Whereas the diazirine group survives almost all chemical operations going on at suitable distances from it, it is very sensitive to all operations producing a partial positive charge at a carbon atom adjacent to the three-membered ring. The oxidation of a-hydroxydiazirines, e.g., 153, succeeds only under very mild conditions and leads to ketones very sensitive toward acids. ° Dilute acid transforms 154 at room temperature with nitrogen elimination to a mixture of cyclopentane carboxylic acid and methylene-cyclopentanone. 

Three-membered rings with two heteroatoms are usually encountered only as reagents. Diazirines are nsefnl carbene precnrsors" - they are generally more stable than the equivalent isomeric diazo compounds, thongh they are sometimes explosive in the pure state. They can be prepared by oxidation of diaziridines that, in tnm, are available via the condensation of a ketone or aldehyde with ammonia and chloramine. Chloro-diazirines, from the reaction of amidines with hypochlorite, wiU undergo Sn2 or Sn2 displacement reactions."" ... 

Most of the work concerning the modification of carbene reactivity has been performed on cyclodextrins (CD) with reactive alkyl carbenes. Diazirines have proven to be the most convenient precursors due to the small size of the three-membered ring and the volatility of the leaving group, molecular nitrogen. Diazirines are usually obtained from the corresponding ketone in two steps in a methanolic solution of ammonia, hydroxylamine-0-sulfonic acid (HOSA) is added yielding a diaziridine which then is oxidized to the diazirine, most conveniently with iodine. 

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