Ynimines as versatile precursors to 2-imido- and 2-amido-1,3-dienes for stereodivergent diels–alder reactions

Abstract

Abstract In contrast to ynamides, whose chemistry has been extensively explored, ynimines remain underutilized in organic synthesis despite their rich functionalities. Here we report a general strategy to access 2-imido-1,3-dienes, synthetically challenging building blocks, through the reaction of ynimines with carboxylic acids. Leveraging this transformation, we develop a three-component reaction of ynimines, carboxylic acids and electron-deficient alkenes that enables the efficient synthesis of 1-imido-3,4- trans -disubstituted cyclohex-1-enes. The sequence proceeds via regioselective hydroacyloxylation and Mumm rearrangement to generate 2-imido-1,3-dienes, which undergo Diels–Alder cycloadditions. An intramolecular variant furnishes trans -fused tricyclic architectures reminiscent of trans -Δ⁹-tetrahydrocannabinol. Chemoselective hydrolysis further converts 2-imido-1,3-dienes into 2-amido-1,3-dienes, enabling chiral squaramide-catalysed enantioselective Diels–Alder reactions to afford 1-amido-3,4- cis -disubstituted cyclohex-1-enes with high stereocontrol. Distinct concerted and stepwise cycloaddition pathways rationalize the observed stereodivergence.