Highly Chemoselective and Enantioselective Synthesis of 3,4-2H-Pyrindin-2-ones by an NHC-Catalyzed [3 + 3] Cyclization

Carbene-catalyzed chemoselective reaction of unsymmetric enedials for access to Furo[2,3-b]pyrroles

A carbene-catalyzed chemoselective reaction of unsymmetric enedials is disclosed. The reaction provides a concise access to bicyclic furo[2,3-b]pyrroles derivatives in excellent selectivity. A main challenge in this reaction is chemoselective reaction of the two aldehyde moieties in the enedial substrates. Mechanistic studies via experiments suggest that our chemoselectivity controls are mostly achieved on the reducing properties of different sited Breslow intermediates. Several side reactions processes and the corresponding side adducts are also studied by high resolution mass spectroscopy analysis. Our method allows for efficient assembly of the furo[2,3-b]pyrrole structural moieties and their analogues widely found in natural products and pharmaceuticals.

N-Heterocyclic Carbene-Catalyzed [3 + 2] Annulation of 3,3'-Bisoxindoles with α-Bromoenals: Enantioselective Construction of Contiguous Quaternary Stereocenters

An NHC-catalyzed enantio- and diastereoselective [3 + 2] annulation of α-bromoenals with bisoxindoles is developed, affording efficient access to various spirocyclic bisoxindole alkaloids. This protocol tolerates a broad substrates scope, with various spirocyclic bisoxindoles obtained in generally excellent enantioselectivities. More importantly, two contiguous sterically congested all-carbon quaternary stereocenters are successfully created during this process.

N-Heterocyclic carbene-catalyzed [3 + 3] annulation of bromoenals with 2-aminochromones to access chromeno[2,3-b]pyridinones

N-Heterocyclic carbene-catalyzed [3 + 3] annulation of bromoenals with 2-aminochromones has been successfully developed. A structurally diverse set of chromeno[2,3-b]pyridinones was efficiently constructed in acceptable to excellent yields. The reaction features mild reaction conditions, a broad substrate scope, and easy scale-up.

Construction of 2-pyridones via oxidative cyclization of enamides: access to Pechmann dye derivatives

An efficient protocol for the construction of structurally diverse 2-pyridone derivatives from imines and α,β-unsaturated acid chlorides in a single operation is reported. The target compounds, including coumarin-8-oxoprotoberbine analogues and lamellarin G isomers, were prepared via thermal cyclization of the in situ generated enamides followed by thermal dehydrogenation. The cyclization of enamides was achieved by the introduction of an electron-withdrawing group on the α-carbon of acid chlorides. This methodology allows quick access to polycyclic Pechmann dyes via rare double oxidative cyclizations of dienamides under mild conditions.

N-Heterocyclic carbene catalyzed asymmetric [3 + 3] cycloaddtion of β,β-disubstituted, α,β-unsaturated carboxylic esters with 3-aminobenzofurans

An NHC-catalyzed β-carbon functionalization reaction to afford enantioenriched benzofuran fused δ-lactams bearing an all-carbon quaternary stereocenter is documented.

Access to dihydropyrano[3,2-b]pyrrol-5-ones skeletons by N-heterocyclic carbene-catalyzed [3+3] annulations

A novel and efficient NHC-catalyzed [3+3] annulation of enals with pyrrol-4-ones was developed, thus providing the dihydropyrano[3,2-b]pyrrol-5-one core structures with broad scope and good to excellent enantioselectivities. Notably, this strategy could also expand to the synthesis of axially chiral compounds and polysubstituted indoles.