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Triethylborane-Initiated Room Temperature Radical Addition of Hypophosphites to Olefins:  Synthesis of Monosubstituted Phosphinic Acids and Esters

Sylvine Deprčle and Jean-Luc Montchamp

*Department of Chemistry, Box 298860, Texas Christian University, Fort Worth, Texas 76129, Email: j.montchamptcu.edu

S. Deprčle, J.-L. Montchamp, J. Org. Chem., 2001, 66, 6745-6755.

DOI: 10.1021/jo015876i


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Abstract

A P-centered radical formation initiated by Et3B/O2 provides phosphinic acid derivatives from hypophosphite salts or esters and alkenes at r.t. under neutral conditions. The reaction tolerates a wide range of functional groups. Monosubstituted phosphinic acids obtained in very good isolated yields by a simple extractive workup, but the isolated yields are diminished if a substituent is polar.

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Details

The document describes a novel and practical method for synthesizing monosubstituted phosphinic acids and esters from hypophosphite salts or esters using triethylborane (Et3B) and oxygen at room temperature. This method contrasts with previous approaches that required peroxide initiators, acid catalysis, and heat, as it operates under neutral conditions, tolerating a wide range of functional groups. The reaction is highly selective for monoaddition, avoiding significant formation of symmetrical dialkyl phosphinates. The process is efficient, yielding products with over 90% purity through simple extractive workup, although yields decrease with polar substituents. The method is limited to electron-rich olefins due to the electrophilic nature of hypophosphite-derived radicals. Additionally, the conditions can be used for the radical reduction of alkyl halides, offering a mild and environmentally friendly alternative to tributyltin hydride. The study also explores the use of alkyl hypophosphites, which, despite being sensitive and thermally unstable, can be employed under these mild conditions to directly produce phosphinate esters. The research opens avenues for further optimization and development of asymmetric versions of the reaction, enhancing the synthesis of functionalized phosphinic acids and esters.


AIBN-Initiated Radical Reactions of Ethyl Phosphinate

M. I. Antczak, J.-L. Montchamp, Synthesis, 2006, 3080-3084.

Palladium-Catalyzed Hydrophosphinylation of Alkenes and Alkynes

S. Deprele, J.-L. Montchamp, J. Am. Chem. Soc., 2002, 124, 9386-9387.


Key Words

phosphinates


ID: J42-Y2001