Lessen rearrangement

The hydroxamic acid function in most alicyclic and aromatic compounds is stable to hot dilute acid or alkali, and derivatives cannot undergo normal base-catalyzed Lessen rearrangement. Di Maio and Tardella," however, have shown that some alicyclic hydroxamic acids when treated with polyphosphoric acid (PPA) at 176°-195° undergo loss of CO, CO.2, or H2O, in a series of reactions which must involve earlj fission of the N—0 bond, presumably in a phosphoryl-ated intermediate. Thus, l-hydroxy-2- piperidone(108) gave carbon monoxide, 1-pyrroline (119), and the lactams (120 and 121). The saturated lactam is believed to be derived from disproportionation of the unsaturated lactam. 

Finally, the Lessen rearrangement provides a practical procedure for replacing the hydroxamic group of a hydroxamic acid (12) by an amino group (14) (equation 2). The initial rearrangement product is an isocyanate (13) which readily reacts with nucleophiles, for example with OH and NH functionalities to give amines (14) and ureas (15). 

Propose a mechanism for the reaction in Equation 11, an example of the Lessen rearrangement. 

The use of the Lessen rearrangement of hydroxamic acids was first brought to bear on this problem by Gallop et al. (1960). The basis of the method is shown in Fig. 4. 

The Lessen rearrangement has been discussed in a general review on hydroxamic acids by Yale (1943). Gallop et al. (1960) studied the reaction with a number of model compounds, poly-a-glutamic acid and an alkali-processedfpigskin gelatin. The dinitrophenylation step allows the... 

Fig. 4. Identification of y-glutamyl and j3-aspartyl residues using the Lessen rearrangement.

Analysis of Material Following Lessen Rearrangement of the Dinitrophenyl Hydroxamate Derivative of Oelalin from Ichthyocol as Compared with the Analysis of a Suitable... 

In the presence of base, acyl derivatives of hydroxamic acids undergo the Lessen rearrangement to yield isocyanates or amines. 

Degradation reactions of carboxylic acids and their derivatives to amines and their derivatives with one less carbon unit involve rearrangements of a carbon to an electron deficient nitrogen atom as key steps, namely the Hofmann Curtius (C), - Schmidt and Lessen rearrangements, as... 

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