Enantioselective synthesis of hexahydrofuro[3,2-c] quinolines through a multicatalytic and multicomponent process. A new “aromatic sandwich” model for BINOL-phosphoric acid catalyzed reactions

Multicomponent and Multicatalytic Reactions – A Synthetic Strategy Inspired by Nature

“…In this process, a butynol derivative, an aldehyde, and an arylamine are combined to afford the heterocyclic product in high yield and enantiomeric excess (Scheme 13). [21] Scheme 13. Multicomponent asymmetric synthesis of furoquinolines by a reaction catalyzed by a gold/BINOL-derived phosphoric acid binary system.…”

Microwave‐Assisted Tandem Organocatalytic Peptide‐Coupling Intramolecular aza‐Michael Reaction: α,β‐Unsaturated N‐Acyl Pyrazoles as Michael Acceptors

“…Additionally, an aromatic sandwich induced by two p-stacking interactions would fix the transition state, thereby promoting the attack of the nitrogen nucleophile on the Si face of the double bond ( Figure 2). [14] In conclusion, an organocatalytic enantioselective IMAMR of sulfonamides bearing a remote a,b-unsaturated pyrazoleamide has been described. Squaramide II was found to be the best catalyst for this transformation that could also be per-formed in a tandem fashion combined with a peptide-coupling reaction.…”

Stereoselective [3+2] Carbocyclization of Indole‐Derived Imines and Electron‐Rich Alkenes: A Divergent Synthesis of Cyclopenta[b]indole or Tetrahydroquinoline Derivatives

“…[1] This formal [4+ +2] cycloaddition reaction between the in situ-formed aryl imine and the electron-rich alkene is believed to proceed throughh ighly asynchronous concerted or stepwise mechanisms. [2] Thus, this reactionm ay be understood as ap rocess initiatedb yaMannich-typea ddition of the enol ether to the activatedi mine followed by capture of the formed oxonium ion by the aniline aromatic ring (Ar 2 ;S cheme 1a). However,i np rinciple, once the oxoniumi ntermediate is formed there is an alternative pathway that involves the aromatic ring comingf rom the aldehyde counterpart (Ar 1 )i nt he second Friedel-Crafts-type step.…”

“…[9,10] The Povarov reactionb etween the imine 6a-HBF 4 complex and 3a to give 7 (a direct precursor of 5)w as characterizeda sa n asynchronous concerted process, in agreement with similarc ycloadditions that were previously reported, in which dihydrofuran 3a was used as dienophile. [2] The asynchronicity of the cycloaddition reactionc an be noted on the forming CÀCb ond lengths at the transition structure (Si face:2 .00 and 3.06 ; Re face:2 .06 and 3.06 , forC 1 ÀC 6 and C 4 ÀC 5 bonds, respectively; Figure 1), [11] which indicate that the C 4 ÀC 5 bond formsa fter formation of the C 1 ÀC 6 bond is almostc omplete. [12] The high asynchronicity is due to distortion of the unsymmetrical diene, as shown by the C 1 -N-C 3 -C 4 dihedral angles (Figure 1) and the impact of catalyst coordination.…”

“…These studies all suggestt hat the Povarov reaction is preferential when HBF 4 is used as catalystb ecause the strong FÀH interactions that this acida llows, along with its acidity,f avor the formation of ah ighly polarized 6a-HBF 4 complex that behaves as av ery good electron-poor dienei ni nverse electrondemandc oncerted[ 4 + +2] cycloadditions. [2] Moreover,t hese FÀ Hi nteractions also favor the formation of compact transition states typical of concerted mechanisms. However,w hen al ess acidic and fluorine-free acid catalyst, such as DPP,i su sed, the concerted Povarov reactionb ecomes less favored.…”