Catalyst-free alcoholysis of phosphane-boranes: a smooth, cheap, and efficient deprotection procedure

Overschelde, Michel Van; Vervecken, Elias; Modha, Sachin G.; Cogen, Simon; Eycken, Erik Van der; Eycken, Johan Van der

doi:10.1016/j.tet.2009.05.063

Cited by 57 publications

(42 citation statements)

References 24 publications

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“…A further advantage of this procedure is the easy deprotection to restore the free phosphane, which is generally accomplished by the use of protic acids [14] or, more conveniently, by reaction with ethanol with heating to reflux. [15] In practice, when 1c (1 equiv.) was treated with nBuLi (2 equiv.)…”

Section: Resultsmentioning

confidence: 99%

“…[16] More recently, the use of alcohols with heating to deprotect borane-phosphorus adducts under neutral conditions has been described. [15] This is a very convenient and mild procedure and was examined with the borane-monophosphane 4, which was easily and quantitatively deprotected by treatment with a mixture of EtOH and THF with heating to reflux for 3 h affording the free monophosphane 5 in quantitative yield (Scheme 2).…”

Section: Resultsmentioning

confidence: 99%

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Tetrathiaheterohelicene Phosphanes as Helical‐Shaped Chiral Ligands for Catalysis

Monteforte¹,

Cauteruccio²,

Maiorana³

et al. 2011

Eur J Org Chem

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Tetrathia[7]helicene-based phosphanes thiaheliphos (2a), nPr-thiaheliphos (2b) and di-nPr-thiaheliphos (2c) have been prepared from the 2,13-dilithio derivatives of thiahelicenes 1a–c by reaction with an excess of Ph2PCl. Protection of the air-sensitive products as BH3 adducts, from which the phosphanes 2a–c are easily regenerated on heating with ethanol, is described. New rhodium(I) complexes 8 and 9 were obtained by reaction of 2c with [Rh(COD)2]+[BF4]– and [BARF]–, respectively, which were converted by oxidation into the chelating phosphane–phosphane oxide RhI complexes 10 and 11. The monophosphane 5 was similarly prepared, andreaction of the dilithio species with ClP(O)(OEt)2 gave the diphosphonate 17, which was characterized by X-ray crystallography. Comparison of data from DFT calculations (B3LYP/SVP) on 2c, 8 and 10 and X-ray data for 17 reveals a strong tension within the thiaheliphos ligands that is partially relaxed by increasing the Rh–P distances and the bite angle of the chelating ligand. Compound (P)-(+)-1c, obtained by chromatographic resolution, was transformed into optically pure (P)-(+)-2c, which was used in the asymmetric hydrogenation of itaconic acid ester and methyl 2-acetamidoacrylate (product ees up to 40%)

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Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

Tetrathiaheterohelicene Phosphanes as Helical‐Shaped Chiral Ligands for Catalysis

Monteforte¹,

Cauteruccio²,

Maiorana³

et al. 2011

Eur J Org Chem

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“…[5] However, the deprotection step can be more problematic, and a number of alternative strategies to achieve this have been reported. [6][7][8][9] Nonetheless, the most commonly applied procedure is still the use of an amine, [3,[10][11][12][13][14][15] which acts as a competing Lewis base to generate the free phosphine R 3 P, and the corresponding amine-borane (R 3 N·BH 3 ) species. A large variety of amines, stoichiometry, solvent, and reaction temperatures have been reported, with some conditions taking several days to reach acceptable levels of conversion.…”

Section: Introductionmentioning

confidence: 99%

Mechanism of Phosphine Borane Deprotection with Amines: The Effects of Phosphine, Solvent and Amine on Rate and Efficiency

Lloyd‐Jones

Taylor

2015

Chemistry A European J

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The kinetics of borane transfer from simple tertiary phosphine borane adducts to a wide range of amines have been determined. All data obtained, including second-order kinetics, lack of cross-over, and negative entropies of activation for reaction of triphenylphosphine borane with quinuclidine and triethylamine, are consistent with a direct (SN 2-like) transfer process, rather than a dissociative (SN 1-like) process. The identities of the amine, phosphine, and solvent all impact substantially on the rate (k) and equilibrium (K) of the transfer, which in some cases vary by many orders of magnitude. P-to-N transfer is more efficient with cyclic amines in apolar solvents due to reduced entropic costs and ground-state destabilisation. Taken as a whole, the data allow informed optimisation of the deprotection step from the stand-point of rate, or synthetic convenience. In all cases, both reactants should be present at high initial concentration to gain kinetic benefit from the bimolecularity of the process. Ultimately, the choice of amine is dictated by the identity of the phosphine borane complex. Aryl-rich phosphine boranes are sufficiently reactive to allow use of diethylamine or pyrrolidine as a volatile low polarity solvent and reactant, whereas more alkyl-rich phosphines benefit from the use of more reactive amines, such as 1,4-diaza[2.2.2]bicyclooctane (DABCO), in apolar solvents at higher temperatures.

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“…1,2-Bis(diphenylphosphino)ethane (IIIp) [16], hexane, 92%. 1,1'-Bis(di-phenylphosphino)ferrocene (IIIq) [26], hexane, 93%. 2,2'-Bis(diphenylphosphino)-1,1'-binaphthalene (IIIr) [16], hexane, 96%.…”

Section: Methodsmentioning

confidence: 99%

Highly efficient reduction of tertiary phosphine oxides and sulfides with amine-assisted aluminum hydrides under mild conditions

et al. 2015

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Reduction of tertiary phosphine oxides and sulfides into the corresponding phosphines with amineassisted aluminum hydrides has been studied. The method is characterized by mild conditions, short reaction time, high efficiency, and expanded substrate scope. The new method is an alternative to the currently used methods of reducing phosphine oxides or recycling phosphines engaged in organic reactions.

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Catalyst-free alcoholysis of phosphane-boranes: a smooth, cheap, and efficient deprotection procedure

Cited by 57 publications

References 24 publications

Tetrathiaheterohelicene Phosphanes as Helical‐Shaped Chiral Ligands for Catalysis

Tetrathiaheterohelicene Phosphanes as Helical‐Shaped Chiral Ligands for Catalysis

Mechanism of Phosphine Borane Deprotection with Amines: The Effects of Phosphine, Solvent and Amine on Rate and Efficiency

Highly efficient reduction of tertiary phosphine oxides and sulfides with amine-assisted aluminum hydrides under mild conditions

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