Hofmann rearrangement oxidative

Treatment of amides with bromine in alkaline medium promotes the Hofmann rearrangement, which may or may not involve a free nitrene intermediate." The oxidation of primary amides with lead tetraacetate and the resulting Lossen rearrangement also produces isocyanates, with the possible intervention of an acylni-... 

Generally, hypervalent iodine reagents are often better than traditional reagents of similar reactivity, with respect to efficiency and chemoselectivity - sometimes even stereoselectivity. Unusual reactivity is another interesting feature which has often resulted in unexpected transformation. Examples of such reactions may be found in the oxidation of nitrogen-containing compounds, the Hofmann rearrangement in acidic conditions, the acetalization of carbonyl compounds in alkali, the remote functionalization of steroids, etc. Some unique transformations were effected in the... 

The oxidative Hofmann rearrangement of primary carboxamides occurs by use of lead tetraacetate (LTA) and several hypervalent organoiodine compounds IF5 (28), PhI(OCOCP3)2 (29), PhI(OH)OTs (30) and PhIO (31) under mildly acidic conditions. 

An example of a reaction that shows this latter regiochemistry is the Hofmann exhaustive methylation, which is sometimes called, rather ambiguously, the Hofmann degradation (this is a term best avoided, because it is sometimes also used to describe the Hofmann rearrangement). In this reaction, an amine is methylated with methyl iodide until the quaternary ammonium iodide is formed. This is then treated with moist silver oxide to convert the iodide to the hydroxide. Write out the final elimination step that occurs on heating. 

Oxidative rearrangement. A reaction related to the Hofmann rearrangement of N-hromoamides occurs on oxidation of an aromatic amide with lead tetraacetate lo give the isocyanate or a derived product in moderate to excellent yield. Simple aliphatic amides react rapidly in dimethylformamide containing triethylamine. 

Organohypervalent iodine(in) compounds are particularly usefiil as the oxidants in the Hofmann-type degradation of aliphatic or aromatic carboxamides to the respective amines [483]. The most common reagents for Hofmann-type rearrangements include (diacetoxyiodo)benzene [484-488], [bis(trifluoroacetoxy)-iodo]benzene [489-494], [hydroxy(tosyloxy)]iodobenzene [495-499] and their recyclable analogs (Chapter 5). The catalytic version of the Hofmann rearrangement using aryl iodides and m-chloroperoxybenzoic acid as terminal oxidant has also been reported (Section 4.1). 

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