Monomeric Phosphazene Bases


Vol. 3, No. 1
Strong and Hindered Bases in Organic Synthesis
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Introduction / Phosphazene Bases / Verkade's Superbases / Traditional bases
Preservation of Reagents / Aldrich Schlenk-Type Glassware

 Phosphazene Bases Introduction / Monomeric Phosphazene Bases (P1)
Dimeric Phosphazene Bases (P2) / Tetrameric Phosphazene Bases (P4)

Monomeric Phosphazene Bases (P2)

Sigma Aldrich offers four monomeric phosphazene bases P1, i.e. 79412, 20025, 79408 and 79432, which differ with respect to their steric hindrance and basicity (Table 1).

Table 1. Order of Basicity of P1 Bases
Order of steric hindrance: P1-t-Oct > BEMP > P1-t-Bu > BTPP
Product Number: 79412 20025 79408 79432
Basicity (MeCNpKBH+): 26.5 27.6 26.9 28.4

All four P1 bases mentioned in Table 1 are distillable liquids and can be easily handled with syringe techniques. Regarding many favorable features they resemble DBU. However, in comparison to DBU (MeCNpKBH+ = 24.3) they are less nucleophilic, far less sensitive towards hydrolysis and 2-4 orders of magnitude more basic.[1] Furthermore, they are particularly suitable for deprotonation (activation) of pronucleophiles. The P1 bases have become important tools e.g. in the field of nucleic acid chemistry,[2,3,4,5] amino acid[6] or peptide synthesis,[7-11] and solid phase chemistry.[12,13] See Table 2 for a list of our P1 bases with their properties, package size etc.

 

Table 2. Phospazene bases P1
79408

Phosphazene base P1-t-Bu

N'-tert-Butyl-N,N,N',N',N'',N''-hexamethylphosphorimidic triamide

tert-Butylimino-tris(dimethylamino)phosphorane

purum, ≥98.0% (NT)   C10H27N4P   Mr 234.3   [81675-81-2]   5 mL, 25 mL


 
79432

Phosphazene base P1-t-Bu-tris(tetramethylene)

BTPP, tert-Butylimino-tri(pyrrolidino)phosphorane

tert-Butylimino-tris(dimethylamino)phosphorane

purum, ≥97.0% (NT)   C16H33N4P   Mr 312.4   [161118-67-8]   5 mL, 25 mL


 

79412

Phosphazene base P1-t-Oct

tert-Octylimino-tris(dimethylamino)phosphorane

purum, ≥98.0% (NT)   C14H35N4P   Mr 290.4   [161118-69-0]   1 mL, 5 mL


 
20025

2-tert-Butylimino-2-diethylamino-1,3-dimethyl-perhydro-1,3,2 diazaphosphorine BEMP

purum, ≥98.0% (GC)   C13H31N4P   Mr 274.4   [98015-45-3]   5mL, 25 mL


 
20026

2-tert-Butylimino-2-diethylamino-1,3-dimethyl-
perhydro-1,3,2-diazaphosphorine on polystyrene

BEMP on polystyrene, capacity base ~2.2 mmol/g   5 g, 25 g


 

Especially interesting for solution phase synthesis and high-throughput chemistry is Merrifield-resin-bound BEMP 20026 (2-tert-Butylimino-2-diethylamino-1,3-dimethyl-perhydro-1,3,2-diazaphosphorine). This base combines the ease of use, separation and recovery of a supported reagent with the outstanding features of BEMP as a base. It is used successfully as a strong and anhydrous base for synthesis with polymeric reagents[17-25] in parallel synthesis.[1]

Applications: The P1 phosphazene bases have a broad application area in organic synthesis. They can be used for alkylation-,[2-6,8-11,13-15,18-27] michael-addition-,[7,12,16,28,29] ester saponification-,[25] acylation-,[30,31] silylations,[32] aldol-condensation-[33] and heterocumulene reactions,[34] as well as in reactions involving transition metals.[35,36] Occasionally, the P1 bases are suitable for E2-eliminations.[17] Among the successfully converted substrates are alcohols,[2,3,25] phenols,[15] thiols,[26,34,35] NH-acidic heterocycles,[2,4,5,14,18,23,24,25] amines,[20,22,30] hydrazones,[21] hydrazids,[34] amides,[36] sulfonamides,[19] malonic esters,[2] benzophenone imines of glycine esters,[6,7,8,13] imides,[9] acetoacetic ester,[16] a-phenylsulfinyl esters,[27] cyano-[12] and isocyanoacetic esters.[11,28,29] Acrylic esters,[27] N-arylamides,[36] dihydrobenzofuranes,[15] pyrroles[28], pyrazoles,[21] 3-thio-1,2,4-triazoles,[34] isoindoles,[29] glycosides[2,26] nucleoside analogues,[4,5,24] and epibatidine[20] have thus been efficiently synthesized.

 

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