/Rotate 0 endobj Reaction with hydrazoic acid forms the protonated azido ketone 2, which goes through a rearrangement reaction with the alkyl group R, migrating over the C-N bond with expulsion of nitrogen. /MediaBox [0 0 595 842] /Contents 59 0 R << 2000 Apr 15;376(2):333-7. doi: 10.1006/abbi.2000.1721. Example 2 A solution of the SM (600 mg, 2.5 mmol) in toluene (10 mL) was cooled in an ice bath under N2 and treated with DPPA (2.06 g, 7.5 mmol) in one portion, followed by DBU (1.14 g, 7.5 mmol). Finally, the acyl azide reacts in the normal manner to give the urethane. The crude product was purified by silica gel column chromatography (eluted with PE) to provide the product as a yellow oil. endobj The dehydration reaction of alcohols to generate alkene proceeds by heating the alcohols in the presence of a strong acid, such as sulfuric or phosphoric acid, at high temperatures. << endobj /Contents 39 0 R 21 0 obj << /MediaBox [0 0 595 842] >> %���� /Resources 36 0 R /S /D /CropBox [0 0 595 842] DPPA undergoes pseudohalogen replacement of the azido group by treatment with nucleophilic reagents, such as ammonia and various amines. << endobj 8 0 obj /Resources 68 0 R /Kids [20 0 R 21 0 R 22 0 R 23 0 R 24 0 R 25 0 R 26 0 R 27 0 R] << /MediaBox [0 0 595 842] /Type /Page << To a suspension of the SM (0.665 g, 1.66 mmol) in THF (10 mL) at RT under Ar was added DPPA (0.400 mL, 1.83 mmol) and DBU (0.297 mL, 1.99 mmol). Since we only have a weak nucleophile and apoor electrophile we need to activate the amide. /Rotate 0 endobj >> 16 0 obj /Resources 48 0 R . /Type /Page /Resources 58 0 R endobj /Rotate 0 /Resources 52 0 R /Outlines 5 0 R /CropBox [0 0 595 842] It is widely used as a reagent in the synthesis of other organic compounds. Protonation of the /CropBox [0 0 595 842] /Parent 7 0 R Research Articles Diphenyl Phosphorazidate (DPPA) − More Than Three Decades Later | TCI /Parent 8 0 R << /CropBox [0 0 595 842] /Resources 66 0 R /MediaBox [0 0 595 842] The reaction mixture was stirred at 0 C for 1 h, then RT for 12 h. The mixture was diluted with EtOAc (100 mL), washed with 2N HCl (2 x 50 mL), brine, dried (Na2SO4), and concentrated. [350 mg, 45%], [Patent Reference: WO2015089337, page 184, (17.5 MB)]. /Contents 45 0 R /Type /Page Upon addition, the newly bound nitrogen atom becomes electron-deficient and is subject to 1,2-migration of a carbon or hydrogen substituent with loss of a molecule of dinitrogen. 20 0 obj stream The resulting mixture was stirred at RT for 18 h. Additional DPPA (0.200 mL, 0.916 mmol) and DBU (0.150 mL, 1.00 mmol) was added and the mixture was stirred at RT for 3 h. The reaction mixture was quenched with sat aq NaHCO3 (30 mL). 11 0 obj endobj /Parent 3 0 R endstream /Contents 47 0 R >> endobj 4 0 obj Adobe PageMaker 6.53 /Type /Pages It is now suggested that this reaction proceeds through the intermediate mixed anhydride, resulting from attack by the nucleophilic carboxylate anion on the phosphorus atom, with expulsion of the azide ion. /Type /Page << /Contents 57 0 R << /Resources 70 0 R /Producer (Acrobat Distiller 4.05 for Macintosh) /MediaBox [0 0 595 842] /PageLabels 6 0 R >> >> << << >> endobj The reaction procedure is quite simple, occurring by refluxing an equimolecular mixture of a carboxylic acid, DPPA, and triethylamine in the presence of a hydroxyl component. >> /Rotate 0 /Resources 56 0 R << /Rotate 0 19 0 obj /CropBox [0 0 595 842] endobj /Parent 7 0 R << Alternatively, the acyl azide can be formed by the direct reaction of a carboxylic acid with diphenylphosphoryl azide (DPPA). /CropBox [0 0 595 842] >> /Parent 7 0 R /Parent 7 0 R << Studies show that DPPA reacts with amines giving the corresponding phosphoramidates; it therefore appears that formation of the amide similarly involves the intermediate anhydride, followed by nucleophilic substitution by the amine. >> << /Type /Page /Rotate 0 /Contents 55 0 R endobj /Rotate 0 >> One way to synthesize alkenes is by dehydration of alcohols, a process in which alcohols undergo E1 or E2 mechanisms to lose water and form a double bond. 13 0 obj /MediaBox [0 0 595 842] /Creator (Adobe PageMaker 6.53) /Rotate 0 , DPPA undergoes pseudohalogen replacement of the azido group by treatment with nucleophilic reagents, such as ammonia and various amines. /Parent 8 0 R stream << /CropBox [0 0 595 842] /Contents 41 0 R The acyl azide is usually made from the reaction of acid chlorides or anydrides with sodium azide or trimethylsilyl azide. 12 0 obj /CropBox [0 0 595 842] /Resources 50 0 R 10 0 obj /Count 10 << %PDF-1.4 DPPA is a coupling reagent with little epimerization (and racemization),1,5aand inactive to the functional groups in the following amino acids:1,7,8 serine (Ser), threonine (Thr), valine (Val), asparagine (Asn), glutamine (Gln), histidine (His), pyroglutamic acid (pGlu), tryptophan (Trp), methionine (Met), S-benzylcysteine (Cys(Bzl)), nitroarginine (Arg(NO2)). endobj The formation of the urethane is particularly valuable since it works with carboxylic acids which fail to undergo the Schmidt reaction, and is believed to involve transfer of the azido group to the carboxylic acid.
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