Expedient Synthesis of 1‐Oxo‐1,2,3,4‐Tetrahydroisoquinoline‐4‐Carboxylates

As a part of the ongoing COVID Moonshot project, an expedient approach to 1‐oxo‐1,2,3,4‐tetrahydroisoquinoline‐4‐carboxylates is described. The method is based on a one‐pot tandem Michael amination–lactamization sequence starting from 2‐(3‐alkoxymethoxy‐3‐oxoprop‐1‐en‐2‐yl)benzoic acids and primary amines. The scope of the N ‐nucleophiles included various aliphatic, aromatic, and heteroaromatic primary amines. The reaction tolerated and was compatible with ether, ester, amide, alcohol, carbamate, free alcohol, azole, or azine moieties. The developed protocol allowed for the preparation of target tetrahydroisoquinoline derivatives in 40%–75% yield on up to 109 g scale (later extended up to 0.86 kg). A mechanistic scheme involving a ring‐chain tautomerism for the electrophilic component of the reaction is proposed. The method was used in the synthesis of DNDI‐6510, a SARS‐CoV‐2 main protease inhibitor that showed promising results obtained in preclinical studies.