期刊
CHEMISTRY-A EUROPEAN JOURNAL
卷 27, 期 55, 页码 13703-13708出版社
WILEY-V C H VERLAG GMBH
DOI: 10.1002/chem.202101788
关键词
pyrazoles; diazophosphonates; dipolar cycloaddition; 1; 5-sigmatropic rearrangements
资金
- BBSRC Doctoral Training Programme [BB/M008770/1]
- EPSRC Centre for Doctoral Training in Sustainable Chemistry [EP/L015633/1]
- University of Nottingham
Diazophosphonates, prepared from alpha-ketophosphonates by oxidation, are useful reagents in 1,3-dipolar cycloaddition reactions for synthesizing N-H pyrazoles. They possess stable properties compared to less stable diazoalkanes, and can migrate during the cycloaddition process.
Diazophosphonates, readily prepared from alpha-ketophosphonates by oxidation of the corresponding hydrazones in batch or in flow, are useful partners in 1,3-dipolar cycloaddition reactions to alkynes to give N-H pyrazoles, including the first intramolecular examples of such a process. The phosphoryl group imbues a number of desirable properties into the diazo 1,3-dipole. The electron-withdrawing nature of the phosphoryl stabilizes the diazo compound making it easier to handle, whilst the ability of the phosphoryl group to migrate readily in a [1,5]-sigmatropic rearrangement enables its transfer from C to N to aromatize the initial cycloadduct, and hence its facile removal from the final pyrazole product. Overall, the diazophosphonate acts as a surrogate for the much less stable diazoalkane in cycloadditions, with the phosphoryl group playing a vital, but traceless, role. The cycloaddition proceeds more readily with alkynes bearing electron-withdrawing groups, and is regiospecific with asymmetrical alkynes. The potential of diazophosphonates for use in bioorthogonal cycloadditions is demonstrated by their facile addition to strained alkynes.
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