Proton sponges catalytic activity

Rodriguez, I., Sastre, G., Corma, A., Iborra, S. Catalytic Activity of Proton Sponge Application to Knoevenagel Condensation Reactions. J. Catai. 1999, 183, 14-23. 

The catalytic activity of proton sponge in the Knoevenagel reaction has been studied227. It was shown that benzaldehyde, in the presence of 2 mol% of 1, reacts with ethyl cyanoacetate and ethyl acetoacetate (equation 22). The condensation is accelerated in polar solvents (especially in DMSO) and does not occur in the case of diethyl malonate, as its CH-acidity is too low (pK = 13.3). 

Although Pd(0) complexes are catalytically active as is, Pd(II) salts have also been used the reducing atmosphere of CO converts Pd(II) to Pd(0) in situ. A proton sponge such as Et3N also must be present to tie up the acidic byproduct, HX. Equations 12.37,77 12.38,78 and 12.3979 provide a few examples of Pd-catalyzed carbonylation. 

Catalytic asymmetric arylation of alkenes.4 This arylation can be effected by a Heck-type arylation of 2,3-dihydrofuran with an aryl triflatc catalyzed by Pd(OAc)2/(R)-BINAP in the presence of 1,8-bis(dimelhylamine)naphthalcnc (proton sponge) as base. This reaction was used to prepare an antagonist (4) of platelet activating factor. 

The first catalytic asymmetric Staudinger reaction to be described used chiral tertiary amines 14 and 15 derived from the Cinchona alkaloids as the nucleophile to activate the ketene via zwitterion formation. The ketene was conveniently generated in situ from the acid chloride. Because the HCl generated in the elimination would consume the chiral tertiary amine catalyst, a nonnucleophilic strong base (e.g.. Proton Sponge) was included to remove the HCl formed. Yields of -lactams were on the order of 60% in 99% ee. 

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