- Synthesis of chiral β-aminophosphine oxides via novel azaboretidinium bromide salts
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The enamino(triphenyl)phosphonium salts [Ph3PCH=CMeNR1R2]+ Br- [where R1 = R2 = (CH2)4, (CH2)5; (S)-CHMePh; R1 = H, R2 = (S)-CHMePh; R1 = H, R2 = (S)-(CH2)3-CH(CH2OH)] have been synthesised and have been shown to react with an excess of borane-tetrahydrofuran to give novel azaboretidinium salts - the first examples of four-membered C-B-N-C heterocycles. The structure of [(1S,3R,4S,1'S)-4-methyl-1-(1-phenylethyl)-1,2-azaboretidin-1-ium-2-uid-3-yl] triphenylphosphonium bromide has been established by X-ray crystallography. Borane does not result in any significant stereoselectivity in these reductions and the azaboretidinium salts are mixtures of diastereomers. In contrast, the similar reduction with (R)-(+)-monoisopinocampheylborane or (S)-(-)-monoisopinocampheylborane leads to single diastereomers in high yields when R1 and R2 are non-bulky; with sterically demanding groups the azaboretidinium salts are unstable and decompose on work-up. Heating these azaboretidinium salts with aqueous sodium hydroxide in methanol, or better, aqueous sodium hydroxide alone, results in the direct formation of the phosphine oxides, Ph2P(O)CH2CHMeNR1R2 which, in the case of compounds derived from IpC2BH2, have an ee value of >75%. In some cases, particularly when R1 and R2 are bulky, the use of sodium hydroxide in methanol results in an appreciable amount of rac-Ph2PCH2CHMe(OMe) as a by-product, but this can be avoided by carrying out the reactions in the absence of methanol.
- Booth, Brian L.,Lawrence, Nicholas J.,Rashid, Humayan S.
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- Formation of P-Ylide under Neutral and Metal-Free Conditions: Transformation of Aziridines and Epoxides to Conjugated Dienes in the Presence of Phosphine
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A general approach to formation of the P-ylide from the reaction of aziridines or epoxides with organophosphine under neutral and metal-free conditions is realized. Conjugated diene derivatives based on this kind of P-ylide were prepared in a facile and c
- Fan, Ren-Hua,Hou, Xue-Long,Dai, Li-Xin
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p. 689 - 694
(2007/10/03)
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- Initial interaction of triphenylphosphonium-2-propenylide with prenal prior to Wittig olefination
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The interaction of triphenylphosphonium-2-propenylide (2) with prenal (6) is shown to proceed via initial C(γ)-C1 addition, followed by dissociation of the coupling product and C(α)-C1 recombination to produce the corresponding betaine, which eliminates triphenyphosphine oxide to yield (E)- and (Z)-6-methyl-1,3,5-triene (7a,b) as the Wittig olefination products.
- Schneider, David F.,Venter, Abraham C.
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p. 3067 - 3081
(2007/10/03)
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- Synthetic potential of the reaction of allylic phosphonium ylides with α, β-unsaturated carbonyl compounds
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The reaction of triphenylphosphonium-2-propenylide (14) with mesityl oxide (9) is shown to proceed via initial Michael addition followed by trans ylidation and an intramolecular Wittig condensation to yield 1,5,5-trimethyl- 1,3-cyclohexadiene (10) as the reaction product.
- Schneider,Venter
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p. 1303 - 1315
(2007/10/03)
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- Synthesis and X-Ray Crystal Structure of (1S,3R,4S,1'S)-4-Methyl-3-triphenylphosphonium-1--2-hydrido-2-borazetidinium Bromide - the First Example of a Four-membered Heterocycle
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The title compound and related derivatives are synthesised from enamino(triphenyl)phosphonium salts and borane, and converted into β-aminophosphonium salts and β-aminophosphine oxides containing two chiral centres.
- Booth, Brian L.,Lawrence, Nicholas J.,Pritchard, Robin G.,Rashid, Humayan S.
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p. 287 - 290
(2007/10/02)
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- Reaction des oxirannes avec la triphenylphosphine en milieu phenolique
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A new access to the vinylphosphonium salts 4 is proposed, using the reaction of epoxides 1 with triphenylphosphine at 100 deg C in phenol.It succeeds very well for the unfunctional epoxides 1 : 2-monosubstituted and 2,3-disubstituted epoxides.In the case of arylepoxides and 2,2-disubstituted unfunctional epoxides, Wittig and " retro-Wittig " side-reactions decrease the yields in vinylphosphonium salts.The reaction of opening epoxides by triphenylphosphine takes place since 40 deg C and is regio and stereoselective.At 40 deg C, the reaction leads to the formation of β-hydroxy alkylphosphonium salts 3.
- Christol, Henri,Grelet, Danielle,Darvich, Mohammad Raouf,Fallouh, Fayez,Plenat, Francoise,Cristau, Henri-Jean
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p. 477 - 483
(2007/10/02)
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