**The Use of Aryl-Substituted Homophthalic Anhydrides in the Castagnoli–Cushman Reaction Provides Access to Novel Tetrahydroisoquinolone Carboxylic Acid Bearing an All-Carbon Quaternary Stereogenic Center**

**Nazar Moshnenko 1, Alexander Kazantsev 1, Olga Bakulina 1, Dmitry Dar'in <sup>1</sup> and Mikhail Krasavin 1,2,\***


**Abstract:** Novel aryl-substituted homophthalic acids were cyclodehydrated to the respective homophthalic anhydrides for use in the Castagnoli–Cushman reaction. With a range of imines, this reaction proceeded smoothly and delivered hitherto undescribed 4-aryl-substituted tetrahydroisoquinolonic acids with remarkable diastereoselectivity, good yields and no need for chromatographic purification. These findings significantly extend the range of cyclic anhydrides employable in the Castagnoli– Cushman reaction and signify access to a novel substitution pattern around the medicinally relevant tetrahydroisoquinolonic acid scaffold.

**Keywords:** homophthalic anhydride; imine; Castagnoli–Cushman reaction; tetrahydroisoquinolone; lactam; all-carbon quaternary atom
