Definitive structural assignment of condensation products from anthranilamide and 3-amino-2-carbamoylthiophene with ketones. Formation of tetrahydroquinazolinones and their thiophene isosteres

Article abstract of DOI:10.1002/jhet.5570350605

Products formed from dehydrative cyclization of cyclopentanone, cyclohexanone, and cycloheptanone with anthranilamide (2) under neutral or acidic conditions are established as the spiro compounds 2,2-polymethylene- 1,2,3,4-tetrahydroquinazolin-4-ones 6 by means of (a) the presence of a ¹³C nmr signal at 66-79 ppm for atom C-2 and (b) X-ray crystallography on the tetramethylene compound 6a. Analogously, products from reactions of these cycloalkanones with 3-amino-2-carbamoylthiophene are now shown by ¹³C nmr spectra to have structures isosteric to 6, i.e. 5,5-polymethylene-4,5,6,7- tetrahydrothieno[2,3-e]pyrimidin-7-ones 5, rather than the chelate ring structures previously proposed. Additionally, conflicting literature reports on product 3 from reaction of acetone with 2 are partially clarified. Correlation of ¹³C chemical shifts in systems 3, 5, and 6 is presented.