Abstract
Zn(II)-catalyzed divergent synthesis of functionalized polycyclic indolines through formal [3 + 2] and [4 + 2] cycloadditions of indoles with 1,2-diaza-1,3-dienes (DDs) is reported. The nature and type of substituents of substrates are found to act as a chemical switch to trigger two distinct reaction pathways and to obtain two different types of products upon the influence of the same catalyst. The mechanism of both [4 + 2] and [3 + 2] cycloadditions was investigated and fully rationalized by density functional theory (DFT) calculations.
Highlights
We began our work by studying the reaction between indole 1a and cyclic 1,2-diaza-1,3-diene 2a (Table S1, Supporting Information (SI))
The wide functional group tolerance was well demonstrated by the fact that both electron-donating (5-OMe, 5, 7-Me) and electronwithdrawing (6-Cl, 5-CO2Me, 5-CN, 5-CHO, 5-NO2) groups were well tolerated, providing efficient access to the fused indoline heterocycles 3e−s
We focused our attention on the reaction of 1,2-diaza-1,3-diene 2n (DD) with 3-methyl indole 1p (In), since such a combination affords both cycloaddition products, i.e.,3ab and
Summary
Functionalized polycyclic fused indoline frameworks are central molecular architectures in nature and pharmaceuticals.. As one of the indolines, C2,C3-fused indolines have attracted extensive research effort over the past decades because scaffolds of this type lead to relatively rigid structures that might be expected to show substantial selectivity in their interactions with enzymes or receptors.. The pyrroloindoline, pyridazino indoline skeletons and their related structures, can be found in numerous natural bioactive products, marketed drugs, and other functional molecules.. The desire to build such appealing polycyclic frameworks, those with bridgehead amino acetal C2 carbons, has inspired the development of elegant methodologies over the past several years. Dearomatization of indoles via cycloaddition reactions has been demonstrated as a reliable approach in converting simple planar aromatic molecules into structurally complex and stereoselective ring systems
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