Lossen degradation

Attempts to initiate formation of a nitrene, and its rearrangement to the iminooxo-phosphorane 80, by subjecting l-chloroamino-2,2,3,4,4-pentamethylphosphetane 1-oxide to a-elimination with sodium methoxide proved unsuccessful48). In contrast, however, the phosphorylhydroxylamides 88 rearrange in the presence of tert-butyl-amine to the heterocumulene 89 and then add base to give the phosphonic diamides 90 (>90%)49). The reaction is reminiscent of the well-known Lossen degradation. 

Substituted imidazole-4,5-dicarbohydroxamic acids on Lossen rearrangement form 1-hydroxyxanthines. Thiazole-4,5-dicarbohydroxamic acids in their partial Lossen degradation, however, show little differentiation between the 4- and 5-position and hence mixtures of the [4,5-d] and the [5,4-d] structures (447) and (448) are formed. The isomer distribution appears to be affected by the solvent as well as by the sulfonyl chloride utilized in the reaction (68JHC331). 

The Lossen degradation was only rarely applied in the synthesis of aminocyclopro-panes. 9 was obtained from 35 by treating with acid or thionyl chloride or by heating the acyl derivatives 36 (equation 9). Especially the potassium salts of 36 required lower temperatures for decomposition than the corresponding sodium or silver salts. ... 

The Hofmann-degradation of acid amides (60-80%, via N-bromoamides) as well as the Lossen-degradation of hydroxamic acids by [l,2,l]-elimination of HBr, or H20, respectively, leads to isocyanates (Scheme 4), which usually yield primary amines RNH2 by solvolysis 36). 

Known examples are the partial Hofmann degradation of pyridine-2,3-dicarbox-amides,134 the Lossen degradation of pyridine-2,3-bis(hydroxamic) acid,135 this giving both possible products, i.e. 3-hydroxypyrido[2,3-(/]pyrimidine-2,4(l//,3//)-dione and 3-hydroxy-pyrido[3,2-d]pyrimidine-2,4(l//,3//)-dione as a 5 1 mixture, and the conversion of a primary carboxamide function into an intermediate isocyanate in the 2-position by oxidation with lead(IV) acetate.136... 

An example is the partial Lossen degradation of pyridine-3,4-bis(hydroxamic) acid, this giving both possible products, i.e. pyrido[4,3-[Pg.204]

This reaction was first reported by Lossen in 1872. It is a thermal or alkaline conversion of hydroxamic acid into an isocyanate via the intermediacy of its O-acyl, sulfonyl, or phosphoryl derivative. In the presence of water, amine, or alcohol, the isocyanate is converted into amine, urea or urethane, respectively. Therefore, this reaction is generally known as the Lossen rearrangement. Occasionally, it is also referred to as the Lossen reaction, Lossen degradation, or Lossen transformation. ... 

Of the classical Hofmann, Curtius, Lossen and Schmidt degradations, only a rare example of the first is known, hypobromite converting 4,7-diamino-2-phenyl-6-pteridinecar-boxamide (208) into 8-amino-2,3-dihydro-6-phenyl-l//-imidazo[4,5-g]pteridin-2-one (209 equation 64) (63JOC1203). 

Determination of pectic structures by specific degradation of pectins, via a carbodiimide 556 mediated Lossen rearrangement on alkaline hydrolysis of galacturonic acid residues 555, was reported (equation 248). 

Lossen rearrangement A modified version of the rearrangement for degradation of carboxylic acids is via reaction of the corresponding acid chloride RCOCl with l-BuOCONHOMs, and subsequent treatment with zinc triflate, 2,6-di-f-butylp)ridine, benzyl alcohol in MeCN. Benzyl carbamates RNHCOOBn are obtained. 

Lossen rearrangement. A modified version of the rearrangment for degradation of carboxylic acids is via reaction of the corresponding acid chlorides RCOCI with... 

This reaction is related to the Hofmann Degradation, Lossen Rearrangement, and Schmidt Reaction. 

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