Photo-Arbuzov rearrangements of benzyl phosphites

Omelanzcuk, J.; Sopchik, Alan E.; Lee, Sueg Geun; Akutagawa, Kunihiko; Cairns, Shayne; Bentrude, Wesley G.

doi:10.1021/ja00228a063

Cited by 35 publications

(20 citation statements)

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“…For example, a solution of bis(phenylmethyl)diazene (BPMDA) (4.8 mg, 0.023 mmol), benzyl dimethyl phosphite, 11 (113 mg, 0.57 mmol), excess [1.1.1]propellane (60−70 μL, approx. 1 mmol), and 100 μL of C 6 D 6 was irradiated for 1 h at 0 °C . The photolysis mixture was diluted to 2.00 mL with C 6 D 6 .…”

Section: Methodsmentioning

confidence: 99%

Free Radical Chain Reactions of [1.1.1]Propellane with Three-Coordinate Phosphorus Molecules. Evidence for the High Reactivity of the Bicyclo[1.1.1]pent-1-yl Radical

Dockery

Bentrude

1997

J. Am. Chem. Soc.

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Three-substituted bicyclo[1.1.1]pent-1-yl radicals (5), generated from additions of radicals to [1.1.1]propellane (1), are found to have high propensities to react with three-coordinate phosphorus molecules. For example, the 3-ethylbicyclo[1.1.1]pent-1-yl radical (5d) reacts with (EtO)3P in a free-radical Arbuzov process to yield dimethyl 3-ethylbicyclo[1.1.1]pent-1-ylphosphonate (13). By contrast, the ethyl radical does not react with (EtO)3P to yield EtP(O)(OEt)2. However, the highly reactive phenyl radical yields PhP(O)(OEt)2. Moreover, attack of the n-pentylbicyclo[1.1.1]pent-1-yl radical (5b) on n-C5H11P(OMe)2 results in a free-radical substitution process that gives dimethyl 3-n-pentyl[1.1.1]bicyclopent-1-ylphosphonite (7b) and the primary alkyl radical n-C5H11 •. Thus, 5 has a propensity to bond to three-coordinate phosphorus that is greater than that of a primary alkyl radical and similar to that of phenyl radical. Reaction of 2-benzyl-4-methyl-1,3,2-dioxaphospholane (9) with 5a is found to proceed with predominant inversion of configuration at phosphorus. Furthermore, 3-phenylmethylbicyclo[1.1.1]pent-1-yl radical, 5a (from reaction of benzyl radical with 1), participates in reasonably efficient radical chain reactions with PhCH2OP(OMe)2 (11) and PhCH2P(OMe)2 (6a) (chain lengths 30−50) to provide structurally novel products of new radical-Arbuzov and radical-substitution reactions. Dimethyl 3-phenylmethylbicyclo[1.1.1]pent-1-ylphosphonate (12) from 11 and dimethyl 3-phenylmethylbicyclo[1.1.1]pent-1-ylphosphonite (7a) from 6a incorporate the bicyclo[1.1.1]pent-1-yl moiety. The high propensity of various 5 to react with three-coordinate phosphorus molecules reflects the highly pyramidal nature of 5 which is accompanied by the increased s-character of the SOMO orbital of 5 and the strength of the phosphorus−carbon bond in the presumed phosphoranyl radical intermediates (3 and 4) formed. Figure depicts the thermodynamics of three classes of free radical substitution and Arbuzov reactions with three-coordinate phosphorus molecules.

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Section: Methodsmentioning

confidence: 99%

Free Radical Chain Reactions of [1.1.1]Propellane with Three-Coordinate Phosphorus Molecules. Evidence for the High Reactivity of the Bicyclo[1.1.1]pent-1-yl Radical

Dockery

Bentrude

1997

J. Am. Chem. Soc.

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“…This laboratory has reported studies of the facile photoinduced Arbuzov rearrangements of dialkyl benzyl phosphites, e.g., 1 → 2 , − and the useful application of this new photoreaction to the synthesis of acyclic nucleoside-based phosphonates. , The quantum yield for formation of phosphonate 2 , Φ P , at 266 nm is 0.43 . At 75% phosphite conversion, the accountability yield of 2 , based on 1 consumed, is 67% and is accompanied by a 3% accountability yield of bibenzyl, PhCH 2 CH 2 Ph .…”

Section: Introductionmentioning

confidence: 99%

“…However, it is clear that were the benzylic carbon of the radical pair 3 or 6 a stereogenic center, loss of stereochemistry at that carbon center would accompany the photorearrangement were it to proceed via a radical pair of sufficient lifetime. Because the chemical yields of phosphonates in photo-Arbuzov reactions are reasonably good, − the stereochemistry in question is of interest from a synthetic, as well as mechanistic, standpoint. This process, if stereoselective, potentially provides an attractive way to introduce, in stereoselective fashion, a stereogenic carbon center of known configuration attached directly to phosphorus.…”

Section: Introductionmentioning

confidence: 99%

Photo-Arbuzov Rearrangements of Benzylic Phosphites. Stereochemistry at Migratory Carbon

1998

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The stereochemistry of the photo-Arbuzov rearrangement of the benzylic phosphite trans-(R,R‘)-10 to the corresponding phosphonate, 11, has been determined by 31P NMR spectroscopy and X-ray crystallography. The reaction is shown to occur with predominant retention of configuration at the stereogenic migratory carbon center of configuration R‘ in starting trans-(R,R‘)-10 and the predominant product cis-(R,R‘)-11. Thus, reaction of optically active phosphoramidite 13 (R/S ratio 98/2, 96% ee) with 1-phenylethanol of high optical purity (R‘/S‘ ratio, 97/3, 94% ee) gives phosphite trans-10 (cis/trans ratio ≥ 97/3) almost entirely as the single enantiomer, trans-(R,R‘)-10. Irradiation of trans-(R,R‘)-10 in acetonitrile with 254 nm ultraviolet light converted it cleanly to two diastereomers of phosphonate cis- 11 in 80/20 ratio (31P NMR). The major (80%) isomer was isolated, recrystallized, and shown by X-ray crystallography to be cis-(R,R‘)-11. The lesser (20%) product is identified, on the basis of its 31P NMR chemical shift, as the diastereomer cis-(R,S‘)-11. (Assignments derived from photorearrangement of totally racemic cis-10 prepared from reaction of racemic 1-phenylethanol with racemic 13.) The generation of trans-(R,S‘)-11 is attributed to the formation (Scheme ) from trans-(R,R‘)-10 of short-lived, predominantly singlet, free radical pairs (12a) that largely (≃80%) undergo combination to form cis-(R,R‘)-11. To a lesser extent (≃20%), the 1-phenylethyl radicals (C) of the pair 12a are converted by rotation to C‘ to generate the stereochemically distinct radical pair 12b that then combines to form cis-(R,S‘)-11. To a first approximation, combination (k comb ) is four times as fast as rotation (k rot ). During the photorearrangement the trans/cis ratios of starting phosphite 10 and product phosphonate 11 are unchanged as is consistent with the generation of phosphinoyl radical B that is configurationally stable at phosphorus.

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“…It has been discovered in our research group that benzyl phosphites readily undergo photochemical Arbuzov rearrangement to benzylphosphonates upon irradiation with UV light [1,2]. The application of this rearrangement to the synthesis of acyclic nucleoside-based phosphonates has been demonstrated [3,4].…”

Section: Introductionmentioning

confidence: 99%

“…CCC 1042-7163/98/020155-06 photorearrangement of 1 showed it to proceed with near exclusive retention of configuration at the chiral carbon when X ‫ס‬ OR [1,5,6]. When X ‫ס‬ NR 2 , however, a higher degree of stereorandomization was observed.…”

Section: Introductionmentioning

confidence: 99%

The photo-Arbuzov rearrangement of dimethyl 9-anthrylmethyl phosphite and the photodimerization of the corresponding phosphonate

et al. 1998

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Photo-Arbuzov rearrangements of benzyl phosphites

Abstract: The thermal Arbuzov rearrangement is a widely known1 reaction of organophosphorus molecules, eq 1. It classically occurs via a two-step mechanism catalyzed by R-X (X = halide, tosylate, etc.) and in certain instances can be autocatalytic.10 Intermolecular

Cited by 35 publications

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Free Radical Chain Reactions of [1.1.1]Propellane with Three-Coordinate Phosphorus Molecules. Evidence for the High Reactivity of the Bicyclo[1.1.1]pent-1-yl Radical

Free Radical Chain Reactions of [1.1.1]Propellane with Three-Coordinate Phosphorus Molecules. Evidence for the High Reactivity of the Bicyclo[1.1.1]pent-1-yl Radical

Photo-Arbuzov Rearrangements of Benzylic Phosphites. Stereochemistry at Migratory Carbon

The photo-Arbuzov rearrangement of dimethyl 9-anthrylmethyl phosphite and the photodimerization of the corresponding phosphonate

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