Carbonylation hydroxamic acid synthesis

On principle, both the hydroxamic acid and the hemiacetal are partially oxidised structures. Thus, the hydroxamic acid should be accessible both fi-om a nitro precursor by reductive cyclisation and from a lactam by N-oxidation (Fig. (7)). Similarly, access to the hemiacetal should e.g. be possible by oxidation of a 2-methylene group as well as by reduction of a 2-carbonyl group, and also by hydrolysis of a 2-haIogen function. The influence of substituents at the aromatic ring on the synthesis of the 1,4-benzoxazinone ring is hardly foreseeable. However, another circumstance has a very rational basis. Due to the fact that the structural instability arises from the cyclohemiacetal (see Fig. (4)) this tmit is prepared at the very end of most syntheses. 

In 1999, the same group applied their cyclization-carbonylation methodology in the synthesis of hydroxamic acids in both solution and solid phase. By using hydroxamates as coupling partners, the corresponding products were formed in good to excellent yields (Scheme 2.32). 

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