Recent advances in the use of phosphorus-centered radicals in organic chemistry

Abstract

This tutorial review aims at presenting recent contributions dealing with organic chemistry of organophosphorus radicals. The first part briefly lays out the physical organic background of such intermediates. In a second part the use of organophosphorus radicals possessing a P-H bond that can undergo homolytic cleavage as alternative mediators is detailed. The third part is focused on radical additions of phosphorus-centered radicals to unsaturated compounds, an old reaction that is being rejuvenated. Lastly, radical eliminations of phosphorus-centered radical are introduced in the fourth part. Most of the latter are relatively novel reactions, and have never been reviewed previously.

Radicals in organic synthesis. Part 1

“…As a result, the last ten years has seen a dramatic increase in the use of such reagents and an excellent overview of this area has recently been published. 14 Probably the most commonly employed phosphorus reagent is the salt, 1-ethylpiperidinium hypophosphite (EPHP), 64,65a-c as exemplified by the formation of tetrahydrofuran 15 (Scheme 6) under relatively mild and clean conditions. 66 An attractive feature of many phosphorus-based reagents is their water solubility, which permits radical reactions to be performed in aqueous media.…”

“…There have been a number of specialist reviews providing comprehensive coverage of various aspects of radical chemistry published over the last five years; topics covered include free-radical cascade processes, 3 the synthesis of heterocycles by radical cyclisations, 4 the synthesis of five-and six-membered heterocycles, 5a,b 5-endo-trig cyclisations, 6 the formation of five-membered rings by translocation-cyclisation, 7 unusual radical cyclisations, 8 radical reactions in aqueous media, 9 the chemistry of ketyl radical anions formed by photoinduced electron transfer, 10 the addition of radicals to C]N bonds, 11,12 'clean' radical reagents, 13 phosphorus-based radical methodology, 14 indium and indium reagents in organic synthesis, 15a,b dichloroindane as a versatile reducing agent, 16 titanocene-mediated radical reactions, 17a,b copper(I)-catalysed atom transfer radical cyclisations, 18 atom transfer radical polymerisations (ATRP), 19a,b samarium(II) iodide in organic synthesis, [20][21][22] samarium(II) iodide in asymmetric synthesis, 23 transition metal generated radicals, 24 cerium regents in synthesis, 25 the persistent radical effect, 26a,b cyclohexa-1,4-diene-based radical reagents, 27 radical additions to aromatic systems, 28 diastereoselective radical reactions, 29a,b enantioselective radical reactions, 30-32 stereoselective conjugate additions. 33,34 radical carbonylations, 35 O-centred radicals in C-O bond formation, 36 inorganic radical reagents, 37 radical chemistry of organoboranes, 38a,b the addition of phosphorus compounds to unactivated hydrocarbons, 39 nitrogen-directed radical rearrangements, 40 thiol-mediated radical cyclisations, 41 the chemistry of N-centred radicals, 42 chirality control in photochemical reactions 43 and the carbometallation of unactivated alkenes by zinc enolate derivatives.…”

Recent Advances in Free Radical Chemistry of C-C Bond Formation in Aqueous Media: From Mechanistic Origins to Applications

“…Following the natures lead, the challenge for today's chemist is to move away from highly volatile and environmentally harmful organic solvents and towards friendly and biologically compatible media [2]. The potential usefulness of free radical reactions in water is demonstrated by ever-increasing studies over the last 5 years [3]. The potential usefulness of free radical reactions in water is demonstrated by ever-increasing studies over the last 5 years [3].…”

Homolytic Substitution at Phosphorus for the Synthesis of Alkyl and Aryl Phosphanes

“…[1][2][3][4][5], except for R = tBu and M = Si where DE add is 3.5 kcal mol À1 (entry 6). This is probably the reason why in the experiment tert-butyl radical was not able to replace SiMe 3 in 1 b in a homolytic substitution reaction.…”