Triflic acid mediated sequential cyclization of ortho-alkynylarylesters with ammonium acetate

A triflic acid (TfOH) mediated sequential cyclization of ortho-alkynylarylesters and ammonium acetate (NH4OAc) was reported. The reaction took place via a Brønsted acid-mediated intramolecular cyclization of ortho-alkynylarylesters followed by an ammonium acetate participated substitution reaction, forming isoquinolin-1-ones as the major products. Different from most of the known synthetic methods of isoquinolin-1-ones, no metal catalyst was required in the reported reaction. The regioisomers – isoindolin-1-ones were obtained together with isoquinolin-1-ones in a few cases. The intermediate compounds – isochromen-1-ones and isobenzofuran-1-ones were also isolated. The interconversion experiments showed that the regioisomers formed during the Brønsted acid induced intramolecular cyclization of ortho-alkynylarylesters. A natural product – ruprechstyril was prepared in a moderate yield employing the new method.