Hydroxamic reactions, review

The following discussion of hydroxamic acids includes saturated systems, e.g., 2, compounds such as 3, derived from aromatic systems, 7V-hydroxyimides such as 7V-hydroxyglutarimide (78), and certain of their derivatives including thiohydroxamic acids. Naturally occurring cyclic hydroxamic acids are discussed to show the range of structural types that has been found, hut macrocyclic polyhydroxamic acids are mentioned very briefly, because several comprehensive reviews of these compounds are already available. The main purpose of this review is to summarize the methods available for the synthesis of cyclic hydroxamic acids, to outline their characteristic reactions, and to present some useful physical data. Their synthesis and some biological properties have previously been reviewed by Coutts. ... 

Enzymatic transformations of alkaloids by peroxidases most probably occur by single-step oxidations catalyzed by the HRP-I and HRP-II forms of the enzyme. The catalysis of one-electron oxidations of compounds containing aromatic hydrocarbon, hydrazine, phenol, hydroxamic acid, and amine functional groups has been recently reviewed (45, 58, 82). A brief summary of those HRP reactions that involve functional groups most commonly occurring in alkaloids is presented below. 

Asymmetric induction using an optically active acrylate ester with O-ethylthiohydroxamate has also been reported (87TL4205). [See reaction (52).] A review on the photolysis and thermolysis of O-hydroxamic thio-... 

The main first part of the review (Section HI) summarizes preparation of hydroxylamine derivatives through alkylation, arylation, and addition reaction of hydroxylamine, or its derivatives such as hydroxamic acids and A-oxysulfonamides. The second main part (Sections IV-VIII) describes methods of creation of hydroxyamino groups de novo from other functionalities. Due to easy interconversion outlined in Section II, syntheses of hydroxylamines and hydroxamic acids are considered together. For the same reason, the chapter also relates to synthesis of A-oxysulfonamides and V-oxyphosphonamides as far as these methods are of interest for the preparation of hydroxylamines. 

The authors do not intend to review aU the reactions that have been reported for the synthesis of hydroxamic acids, but rather to limit the section to the most relevant studies which have appeared in the literature in recent years. 

This review describes electrochemical reactions of hydroxylamines, oximes and hydroxamic acids. In addition, utilization of hydroxylamines and hydroxamic acids as redox mediators are shown. Since the electroorganic chemistry of hydroxylamines, oximes and hydroxamic acids is rather a minor area in the electrochemistry of organic compounds, the reader is advised to refer to texts which are written for organic chemists unfamiliar with the electroorganic chemistry. 

A previous review has highlighted the following methods of ring synthesis intramolecular cyclization of oximes, nitro alkenes, and nitrones, and [4+2] cycloaddition reactions <1996CHEC-II(6)279>. In addition to that, this review includes the intramolecular cyclization of hydroxylamines, hydroxamates, hetero-Diels-Alder [4+2], 1,3-dipolar cycloaddition of nitrile oxides to alkenes, and [3+3] cycloaddition reactions. This review does not cover cycloaddition reactions of the [4+2] [3+2] and [4+2] [3+2] [3+2] types which primarily led to heterocycle-fused oxazine ring systems. 

An alternative approach applicable both to the synthesis of racemic aspergillic acid428 and neoaspergillic acid is illustrated by the synthesis (Scheme 50) of neoaspergillic acid (8).429 The initial reaction of dl-leucine anhydride (235) with phosphoryl chloride produces, in addition to the required monochloro compound (236), some dichloro compound (237), and flavacol (4). Reaction of the latter compound with a mixture of phosphoryl chloride and phosphorus pentachloride yields further 2-chloro-3,6-diisobutylpyrazine (236). The remaining steps of the synthesis involve reactions discussed previously in this review, with the exception that the hydroxamic function is protected by diazomethane methylation and finally regenerated by ethanolic hydriodic acid treatment.429... 

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... 

When the reaction of an aminophenol with A -ethoxycarbonylthioamide or a dithioate ester is applied to an aminothiophenol, a high yield of benzothiazole is obtained [2860, 2899]. The same substrate is converted into a benzothiazole efficiently at ambient temperature with hydroxamoyl chloride (the chloride of a hydroxamic acid) [3468]. Similar compounds in which the 2-phenyl group is varied are of interest as dye intermediates and are synthesized from quinonoid aminothiols [3477] the chemistry of quinonoid heterocyclcs has been reviewed [2947, 3650]. 

Five reviews have appeared entitled A mechanistic investigation of gelation. The sol-gel polymerization of precursors to bridged polysilsequioxanes , which contains Si NMR data, Derivatives of hydroxamic acids , which contains Si NMR data, A primer on the aqueous chemistry of silicon , which contains Si NMR data, Organotin(IV) complexes of amino acids and peptides , which contains Sn NMR data, and Novel reaction system using highly coordinated organotin enolates . ... 

This reaction, known as the Lossen rearrangement, has seen but little synthetic application 2 . ito possesses no distinct advantages over the Curtius, Hofmann, and Schmidt reactions. It appears to be useful when hydroxamic acids result as primary products. The reaction has been reviewed recently. 

---