Unlike the carbocyclic products of traditional dienes and dienophiles, the Diels-Alder cycloadducts of N-aryl-N'-carbamoylnitroso species and dienes are thermally labile under relatively mild conditions below 100 �C. The rate of the retro Diels-Alder reactions of these N-carbamoyl-3,6-dihydro-1,2-oxazine adducts is particularly convenient to measure because the nitroso heterodienophile is hydrolytically unstable and decomposes to CO2, HNO, and a free aniline.  The use of 1H NMR spectroscopy to track the appearance of the aniline has proven the most versatile for the monitoring of this reaction.  However, with the careful choice of N-(4-nitrophenyl)-N'-hydroxyurea as the nitroso dienophile precursor, the reaction rate of the rate-determining retro-cycloaddition step can be tracked colorimetrically.  As such, diene substituent effects have been probed at temperatures between 35 and 90?�C.   Analogously, use of a diene chromophore has enabled the elucidation of the effects of aryl subsitutents on the nitroso dienophile. Extensions to other heterodienophiles (such as azo compounds) will be assessed.

Retro-hetero-Diels-Alder reactions: Probing the effects of diene and nitroso heterodienophile substitution on the rates of retro-cycloadditions

247th National Meeting (2014)

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