Chiral Isochalcogenourea-Catalysed Enantioselective (4+2) Cycloadditions of Allenoates

Angew Chem Int Ed Engl. 2024 Jan 8;63(2):e202315345. doi: 10.1002/anie.202315345. Epub 2023 Dec 11.

Abstract

Allenoates are versatile building blocks which are primarily activated and controlled using chiral tert. phosphine and tert. amine Lewis bases. We herein report the first example of allenoate activation by using chiral isochalcogenoureas (IChU) for formal (4+2) cycloaddition reactions. Compared to established phosphine and amine catalysis, the use of these easily available Lewis bases enables new stereoselective reaction pathways proceeding with high enantioselectivities, diastereoselectivities, and in good yields. In addition, the factors governing enantioselectivity and the origin of the observed differences compared to other commonly used Lewis bases are explained.

Keywords: Allenoates; Cycloadditions; DFT Calculations; Lewis Bases; Organocatalysis.