Tetrahydroquinolines by the multicomponent Povarov reaction in water: calix[n]arene-catalysed cascade process and mechanistic insights

Abstract

A new calixarene-catalyzed cascade process, via the Povarov reaction, for the synthesis of tetrahydroquinolines is described, and the proposed reaction mechanism was validated.

Diels–Alder Cycloaddition Reactions in Sustainable Media

“…The aforementioned MCPRs can be classified into ABC and ACC', referring to the classical conditions (aniline, aldehyde and nucleophilic alkenes) and the use of aniline and two equivalents of a nucleophilic alkene, respectively. One example of the latter, the synthesis of furano[3,2-c]-1,2,3,4-tetrahydroquinolines involving the MCPR between anilines 2 and two equivalents of 2,3-dihydrofuran (6), has been recently reported by Fernandes and coworkers (Scheme 50) [138]. Using water as solvent and p-sulfonic acid calix [4]arene (CX4SO 3 H) as organocatalyst, a series of tetrahydroquinoline derivatives 214 were prepared in moderate to excellent yield, with aniline and 4-halo-anilines providing the target products in the highest yields (85-95%).…”

Calix[n]arenes in Action: Recent Applications in Organocatalysis

“…In some cases, the reaction was diastereoselective with dr values of 68 : 32 trans/cis , 69 : 31 cis / trans , but no correlation could be established for cis or trans selectivity as a function of the substituent groups and assessed conditions. Again, when PHSA was used as a catalyst under the same reaction conditions, the yield was lower (89 %) than the one found for the macrocycle [59] …”

“…The Povarov reaction catalyzed by CX34 can be modulated to provide other N ‐heterocycles, such as 1,2,3,4‐tetrahydroquinolines and quinolines [59,60] . In 2019, Fernandes et al .…”

“…developed a protocol for the synthesis of furano[3,2‐ c ]‐1,2,3,4‐tetrahydroquinolines using CX34 as a catalyst with a concentration of 4 mol%, in water, at 70 °C for 5 hours, using different substrates N ‐aryl amines and 2,3‐dihydrofuran in a molar ratio 1 : 2 (Table 26). [59] …”

Sustainable synthesis of acetals from glycerol as potential additives for biofuels under solvent-free conditions

“…18,20 Furthermore, there is the fact that the active phase (CX4SO 3 H) has already been reported to exhibit excellent catalytic activity in numerous chemical processes. 21–30…”