Nucleophilic and acid catalysis in phosphoramidite alcoholysis



: Nurminen EJ, Mattinen JK, Lonnberg H

Publisher: ROYAL SOC CHEMISTRY

: 2001

Journal of the Chemical Society, Perkin Transactions 2

JOURNAL OF THE CHEMICAL SOCIETY-PERKIN TRANSACTIONS 2

: J CHEM SOC PERK T 2

: 11

: 2159

: 2165

: 7

: 1472-779X

DOI: https://doi.org/10.1039/b104910k


Numerous triflates, mesylates,dagger chlorides, trifluoroacetates and tetrazolides of trialkylammonium, pyridinium and azolium ions have been studied as activators for the reaction of N,N,O,O'-tetraisopropylphosphoramidite with propan-2-ol in acetonitrile. The progress of the reactions was followed by P-31 NMR spectroscopy, and the pK(a) values of the activators were determined by a C-13 NMR spectroscopic method based on competing simultaneous protonation of two bases. The salts promoted the reaction both as acids and nucleophiles, the acidity playing a more important role than the nucleophilicity. The Bronsted a value for the general acid catalysis was observed to range from 0.6 to 0.9 and the beta (nucl) value to be 0.2 (pK(a) of the conjugate acid used as the measure of nucleophilicity). Mixtures of neutral azoles or pyridines and weakly acidic ammonium salts were also shown to be useful activators that allow the acidity and nucleophilicity to be tuned independently of each other.



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