Benzohydroxamic Acid

[495-18-1]  · C7H7NO2  · Benzohydroxamic Acid  · (MW 137.14)

(precursor to benzoyl nitroso compounds and used in the synthesis of a wide range of heterocyclic compounds1)

Physical Data: mp 125 °C.

Solubility: sol water; slightly sol other organic solvents.

Form Supplied in: solid; widely available.

Benzohydroxamic acid shows considerable reactivity towards various functional groups. For example, reaction of this reagent with certain alkynic compounds gives 1,3-oxazoles in good yields (eq 1).1 Benzohydroxamic acid can also be used as a precursor to the Lossen rearrangement (eq 2).2

Oxidation of benzohydroxamic acid with Pr4N+IO4- in DMF at 23 °C generates a transient benzoylnitroso compound. If the oxidation is carried out in the presence of a diene, cycloaddition products are formed in high yields (eqs 3-5). For example, oxidation in the presence of cyclohexadiene gives a [2.2.2] bicyclic adduct.3 Reductive cleavage of the N-O bond of the cycloadduct with the preservation of both the double bond and the amide carbonyl can be readily accomplished in quantitative yield by treating the adduct with an excess of Aluminum Amalgam in THF-H2O at 0 °C.

Eq 6 details the result of a study of the regioselectivity of the [4 + 2] cycloaddition of PhCONO with a 2-substituted 1,3-cyclohexadiene.4 The ratio of regio adducts is not affected by change in the reaction solvent, temperature, or the source of the nitroso compound.


1. Chen, F. M. F.; Forest, T. P. CJC 1973, 51, 1368.
2. Bauer, L.; Pihuleac, J. S 1989, 1, 61.
3. (a) Keck, G. E.; Fleming, S. A. TL 1978, 4763. (b) Kirby, G. W.; Mackinson, J. JCS(P1) 1985, 883. (c) Kirby, G. W.; Sweeny, J. G. CC 1973, 704. (d) Kirby, G. W.; Mackinson, J. JCS(P1) 1985, 887.
4. Boger, D. L.; Patel, M.; Takusagawa, F. JOC 1985, 50, 1911.

Gary E. Keck & Anandan Palani

University of Utah, Salt Lake City, UT, USA



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