On the use of empirically corrected theoretical procedures in preparative chemistry: Synthesis, spectroscopic and theoretical studies on 1,3-bis(trimethylsilyl)benzimidazol-2-one

The present work demonstrates the utility of the extended DFT-derived scaled quantum mechanical (SQM) force fields for predicting the product of a chemical synthesis, namely the reaction of 1,3-dihydrobenzimidazol-2-one with BSTFA [N,O-bis(trimethylsilyl)trifluoro-acetamid]. Since the reactant has two tautomeric forms, the structure of product of the silylation reaction is not obvious. The calculated force fields of the potentially possible products were determined at the B3-LYP/6-31G* level and scaled by transferable scale factors obtained from the literature. The calculated SQM infrared (IR) spectra were numerically compared with the experimental IR spectrum of the product of the reaction. Several proximity measures (S scalar product, residual R-factor, and the standard RMS) between the calculated and experimental IR spectra have been calculated concluding that the product of the reaction is 1,3-bis(trimethylsilyl)benzimidazol-2-one. The NMR spectra of the product gave an independent validation of this result. The presented algorithmic method is able to form a basis for a more automatic procedure, e.g., in the field of the combinatorial syntheses. The S-factor seems to be the most useful proximity measure between a calculated and an experimental spectrum.