Abstract:A novel tandem Mannich/intramolecular aminal formation between tryptamines and salicylaldehydes was reported. This strategy provides a promising approach for the stereoselective synthesis of a range of complex fused spiroindolines, which bear a highly congested contiguous spiro quaternary center and two tertiary stereocenters, in a highly economical and effective fashion.
“…Bearing in mind that the formation of tetrahydro β-carbolines occurs through the Pictet–Spengler reaction, − we envisaged that the regeneration of the latent N -acyliminium ion (B′) in type A′ dipeptides could provide access to the corresponding aminoacetal derivatives (C′) via α-functionalization of the amine (Scheme ). − …”
An acid- and oxidant-promoted intramolecular cyclization of a tetrahydro-β-carboline-based dipeptide has been developed to prepare new indole-fused aminoacetals. This approach involves N-acyliminium formation from readily available precursors and cyclization under mild reaction conditions. The diastereoselectivity in the formation of the products is influenced by the specific substituents of the starting reagents, which has been rationalized analyzing the energy profile of the related reactions and the relative stability of the proposed structures based on DFT computational methods.
“…Bearing in mind that the formation of tetrahydro β-carbolines occurs through the Pictet–Spengler reaction, − we envisaged that the regeneration of the latent N -acyliminium ion (B′) in type A′ dipeptides could provide access to the corresponding aminoacetal derivatives (C′) via α-functionalization of the amine (Scheme ). − …”
An acid- and oxidant-promoted intramolecular cyclization of a tetrahydro-β-carboline-based dipeptide has been developed to prepare new indole-fused aminoacetals. This approach involves N-acyliminium formation from readily available precursors and cyclization under mild reaction conditions. The diastereoselectivity in the formation of the products is influenced by the specific substituents of the starting reagents, which has been rationalized analyzing the energy profile of the related reactions and the relative stability of the proposed structures based on DFT computational methods.
The synthesis of chromeno[2,3-b]indole from simple starting materials remains a demanding process. Herein, 2-bromoindole undergoes nucleophilic attack from salicylaldehyde, followed by intramolecular insertion of an aldehyde group and aromatization to generate the desired chromeno[2,3-b]indoles. Moreover, various functional groups were tolerated and a gram-scale synthesis of the product could be achieved under the optimized condition.
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