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Verkade S 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

Verkade's bases

Verkade's bases, football-shaped proazaphosphatrane molecules of type 1, are very strong bases due to the extraordinary stability of 2 when 1 reacts with a proton.

Due to the stability of the protonated form 2, Verkade's bases are about eight orders of magnitude stronger as a Lewis base than any amine known, including the prominently used DBU, DBN and Proton Sponge. (14795).

Applications: Verkade's bases have been successfully applied in a variety of organic reactions, such as alkylations, dehydrohalogenations, acylations,[1] a variety of condensation and organometallic reactions for carbon-carbon bond formation.[2] A second characteristic of the novel cage molecules of type 1 is their ability to act as a superior catalyst for a continuously widening range of reactions[3-6] such as protecting alcohol groups with various silyl groups during multistep syntheses,[4] trimerizing isocyanates to isocyanurates[5] and the synthesis of alpha, beta-unsaturated nitriles.[6].

Table 7. Verkade's bases

55,695-5

2,8,9-Triisopropyl-2,5,8,9-tetraaza-1-phosphabicyclo[3.3.3]undecane

2,5,8,9-tetraaza-1-phosphabicyclo[3.3.3]undecane,2,8,9-tris(1-methylethyl)]

C15H33N4P   Mr 304.3   [175845-21-3]   1g, 5g


 

56,588-1

2,8,9-Triisobutyl-2,5,8,9-tetraaza-1-phosphabicyclo[3.3.3]undecane

Purity ~97%   C18H39N4P   Mr 342.51   [331465-71-5]   1g, 5g


 

References:

  1. S. Arumugam, D. McLeod, J. G. Verkade, J. Org. Chem., 1997, 62, 3677.
  2. B. D'Sa, P. B. Kisanga, J. G. Verkade, J. Org. Chem., 1998, 63, 3691.
  3. P. B. Kisanga, B. D'Sa, J. G. Verkade, J. Org. Chem., 1998, 63, 10057.
  4. B. D'Sa, J. G. Verkade, "P(MeNCH2CH2)3N: An Efficient Silylation Catalyst," J. Am. Chem. Soc., 1996, 118, 12,832.
  5. J.-S. Tang, J. G. Verkade, "P(MeNCH2CH2)3N as a Superior Catalyst in the Conversion of Isocyanates to Isocyanurates," Angew. Chem., Int. Ed. Engl., 1993, 32, 896.
  6. P. B. Kisanga, J. G. Verkade, J. Org. Chem., 1999, 64, 4298.