Non-metal Lewis acid-catalyzed cross-Claisen condensation for β-keto esters

In this work, we disclose a new catalytic and highly chemoselective cross-Claisen condensation of esters. In the presence of TBSNTf₂ as a non-metal Lewis acid, various esters can undergo cross-Claisen condensation to form β-keto esters which are important building blocks. Compared with the traditional Claisen condensation, this process, employing silyl ketene acetals (SKAs) as carbonic nucleophiles to achieve cross-Claisen condensation, requires mild conditions and has good tolerance of functional groups.

Nucleophilic Halogenation of Cyclic Nitronates: A General Access to 3-Halo-1,2-Oxazines

In this article, comprehensive studies on the nucleophilic chlorination and bromination of readily available six-membered cyclic nitronates (1,2-oxazine-N-oxides) are reported. Under optimized conditions (POCl₃ or (COBr)₂ with Hünig's base), 3-halo-substituted 1,2-oxazines, which are difficult to access by other routes, were obtained in good to high yields. The latter were shown to be convenient precursors to other 3-substituted 1,2-oxazine derivatives using Lewis/Brønsted acid-assisted substitution of the halide atom for C-, S-, and N-nucleophiles.

Insights into the isothiourea-catalyzed asymmetric [4 + 2] annulation of phenylacetic acid with alkylidene pyrazolone

A computational study on the isothiourea-catalyzed asymmetric [4 + 2] annulation of phenylacetic acid with alkylidene pyrazolone was performed using the DFT method.

Direct enantioselective C-acylation for the construction of a quaternary stereocenter catalyzed by a chiral bicyclic imidazole

A direct enantioselective C-acylation of benzofuranones was developed using a chiral bicyclic imidazole catalyst and an achiral tertiary amine additive.

Enantioselective (4+2) Annulation of Donor-Acceptor Cyclobutanes by N-Heterocyclic Carbene Catalysis

Herein we report the enantioselective (4+2) annulation of donor-acceptor cyclobutanes and unsaturated acyl fluorides using N-heterocyclic carbene catalysis. The reaction allows a 3-step synthesis of cyclohexyl β-lactones (25 examples) in excellent chemical yield (most ≥90 %) and stereochemical integrity (all >20:1 d.r., most ≥97:3 e.r.). Mechanistic studies support ester enolate Claisen rearrangement, while derivatizations provide functionalized cyclohexenes and dihydroquinolinones.

Catalytic Enantioselective Synthesis of C1 - and C2 -Symmetric Spirobiindanones through Counterion-Directed Enolate C-Acylation

A catalytic enantioselective route to C1 - and C2 -symmetric 2,2'-spirobiindanones has been realized through an intramolecular enolate C-acylation. This reaction employs a chiral ammonium counterion to direct the acylation of an in situ generated ketone enolate with a pentafluorophenyl ester. This reaction constitutes the first example of a direct catalytic enantioselective C-acylation of a ketone and provides an efficient and highly enantioselective route to axially chiral spirobiindanediones. These products can be diastereoselectively derivatized, offering access to a range of functionalized spirocyclic architectures.

Ni-Catalyzed Enantioselective C-Acylation of α-Substituted Lactams

A new strategy for catalytic enantioselective C-acylation to generate α-quaternary-substituted lactams is reported. Ni-catalyzed three-component coupling of lactam enolates, benzonitriles, and aryl halides produces β-imino lactams that then afford β-keto lactams by acid hydrolysis. Use of a readily available Mandyphos-type ligand and addition of LiBr enable the construction of quaternary stereocenters on α-substituted lactams to form β-keto lactams in up to 94% ee.

Isothiourea-mediated one-pot synthesis of functionalized pyridines

Acids to bases: The synthesis of 2,4,6-trisubstituted pyridines from (phenylthio)acetic acid and a range of α,β-unsaturated ketimines is reported. This process proceeds by intermolecular Michael addition/lactamization, thiophenol elimination, and N- to O-sulfonyl migration, giving 2-sulfonate-substituted pyridines which are readily derivatized to generate structural diversity.