A simple monomeric tungstate, TBA2[WO4] (I, TBA = tetra-n-butylammonium), could act as an efficient homogeneous catalyst for chem. fixation of CO2 with 2-aminobenzonitriles to quinazoline-2,4(1H,3H)-diones. Various kinds of structurally diverse 2-aminobenzonitriles could be converted into the corresponding quinazoline-2,4(1H,3H)-diones in high yields at atm. pressure of CO2. Reactions of inactive 2-amino-4-chlorobenzonitrile and 2-amino-5-nitrobenzonitrile at 2 MPa of CO2 also selectively proceeded. The present system was applicable to a g-scale reaction of 2-amino-5-fluorobenzonitrile (10 mmol scale) with CO2 and 1.69 g of anal. pure quinazoline-2,4(1H,3H)-dione could be isolated. In this case, the turnover no. reached up to 938 and the value was the highest among those reported for base-mediated systems so far. NMR spectroscopies showed formation of the corresponding carbamic acid through the simultaneous activation of both 2-aminobenzonitirile and CO2 by I. Kinetic and computational studies revealed that I plays an important role in conversion of the carbamic acid into the product. [on SciFinder(R)]
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