Syntheses and Reactions of Pyrroline, Piperidine Nitroxide Phosphonates.

Mostafa Isbera,József Jekő,Balázs Bognár,Kálmán Hideg,Cecilia Sár,Tamás Kálai

doi:10.3390/molecules25102430

Mostafa Isbera, József Jekő + Show 4 more

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https://doi.org/10.3390/molecules25102430

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Abstract

Organophosphorus compounds occupy a significant position among the plethora of organic compounds, but a limited number of paramagnetic phosphorus compounds have been reported, including paramagnetic phosphonates. This paper describes the syntheses and further transformations of pyrroline and piperidine nitroxide phosphonates by well-established methods, such as the Pudovik, Arbuzov and Horner-Wadsworth-Emmons (HWE) reactions. The reaction of paramagnetic α-bromoketone produced a vinylphosphonate in the Perkow reaction. Paramagnetic α-hydroxyphosphonates could be subjected to oxidation, elimination and substitution reactions to produce various paramagnetic phosphonates. The synthesized paramagnetic phosphonates proved to be useful synthetic building blocks for carbon-carbon bond-forming reactions in the Horner-Wadsworth-Emmons olefination reactions. The unsaturated compounds achieved could be transformed into various substituted pyrroline nitroxides, proxyl nitroxides and paramagnetic polyaromatics. The Trolox® equivalent antioxidant capacity (TEAC) of new phosphonates was also screened, and tertiary α-hydroxyphosphonatate nitroxides exhibited remarkable antioxidant activity.

Highlights

Functionalized phosphonates are fascinating organophosphorus compounds used in biology, pharmacology, agriculture and organic chemistry [1,2,3]
We report the syntheses of new pyrroline and piperidine nitroxide phosphonates starting from nitroxide halogenides, acetylenes, aldehydes and ketones
The Arbusov, Pudovik, Perkow and HWE reactions were adopted to access paramagnetic allylic, vinyl, acetylene- and α-hydroxyphosphonates or vinyl phosphates, giving the desired products with moderate to good yields. α-hydroxyphosphonates could be further transformed by oxidation, substitution or elimination reactions

Summary

Introduction

Functionalized phosphonates are fascinating organophosphorus compounds used in biology, pharmacology, agriculture and organic chemistry [1,2,3]. Perkow reactions [7], these reactions were applied limitedly to access paramagnetic phosphorus compounds, many phosphorus containing nitroxides have been published [8,9,10,11]. Remarkable part of these materials are mainly 2-substituted β- or γ-phosphorylated five-membered nitroxides exhibiting a second notably large hyperfine splitting with the one-half spin nucleus of the phosphorus atom [12,13,14,15,16] (Figure 1). Our purpose was to evaluate the scope and limitations of the reactions of the newly synthesized paramagnetic phosphonates or α-hydroxyphosphonates as potential

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