Tropine-based dicationic molten salt: An active catalyst in the acceleration of one-pot synthesis of spiro-2-amino-4H-pyran-oxindoles and bis-2-amino-4H-pyrans

Abstract

A suitable dicationic molten salt based on tropine ([(Tropine)2C3H5OH].2Cl) was prepared and characterized by FT-IR, 1H-NMR, 13C-NMR, FESEM, CHN, MS and TGA analysis methods. To determine the accurate structure of the catalyst the potential energy surfaces of possible pathways have been explored and the corresponding energy barriers and some of the required NMR chemical shifts have been calculated. On the basis of the Curtin-Hammett principle, Min4bb seems likely to be the main structure and by the comparison of the experimental and calculated NMR chemical shifts, its structure has been elucidated. The calculations have been performed at the DFT (B3LYP) computational levels with a combination of 6-31+G(d,p) and 6-311G(d,p) basis sets. In continue the application of reagent was investigated in the acceleration of the synthesis of bis-2-amino-4H-pyrane and spiro-2-amino-4H-pyran-oxindole derivatives. The considerable features of the introduced procedure are included easy preparation of the catalyst, use of small amounts of the catalyst and simple work-up method. Also, the catalyst can be easily recovered and recycled for at least 5 times.