Enantioselective [3 + 2] Annulation of Enals with 2-Aminoacrylates Catalyzed by N-Heterocyclic Carbene

γ-Lactam synthesis from cyclobutanone via transoximation and the Beckmann rearrangement

This manuscript describes the synthesis of γ-lactam from the nitrogen insertion reaction of cyclobutanones using an oxime as an aminating reagent with a catalytic amount of Brønsted acid. This method was employed with a more stable oxime reagent, which is a precursor analog of hydroxylamine derivatives with explosive properties. The reaction was tolerated by various substituted cyclobutanones and less strained five- or six-membered ketones. The obtained γ-lactam products could be transformed into γ-aminobutyric acid derivatives via ring-opening hydrolysis. The reaction mechanism is discussed from the perspective of the isotope effect, etc.

Highly enantioselective δ-protonation and formal [3 + 3] annulation promoted by N-heterocyclic carbene

A chiral NHC catalyst reacts with α,β-γ,δ-diunsaturated aldehydes to generate an extended Breslow intermediate. Upon δ-protonation and tautomerization, the resulting α,β-unsaturated acyl azolium undergoes [3 + 3] annulation with enamines to afford various dihydropyridinones.

The N-heterocyclic carbene-catalyzed [3 + 2] annulation of isoindigos with enals: the enantioselective construction of three contiguous stereogenic centers

An NHC-catalyzed enantioselective [3 + 2] annulation of enals and isoindigo is introduced as an efficient strategy for the construction of dimeric spirocyclic bisindoline alkaloid derivatives with moderate yields and good enantioselectivities.

Brønsted Base-Catalyzed Formal Reductive [3+2] Annulation of 4,4,4-Trifluorocrotonate and α-Iminoketones

A formal reductive [3+2] annulation of 4,4,4-trifluorocrotonate and α-iminoketones was developed under Brønsted base catalysis. A single phosphazene base efficiently catalyzes the one-pot tandem reaction involving two mechanistically different elementary processes, namely the chemoselective reduction of an imine moiety of α-iminoketones with thiols as the reductant and the subsequent intermolecular Michael addition of an enolate of α-aminoketones concomitant with lactam formation. This operationally simple method provides β-trifluoromethyl-substituted γ-lactams with a tetrasubstituted carbon as a single diastereomer.

Asymmetric synthesis of γ-lactams under low-loading N-heterocyclic carbene catalysis

Low-loading N-heterocyclic carbene-catalyzed oxidative formal [3 + 2] annulation of enals with N-Ts diethyl aminomalonate has been successfully developed.

Asymmetric Synthesis of Oxindole-Derived Vicinal Tetrasubstituted Acyclic Amino Acid Derivatives by the Mannich-Type Reaction

The catalytic asymmetric Mannich-type reaction of 3-hydroxy/3-aminooxindoles with 2-aminoacrylates to afford oxindole-derived acyclic amino acid derivatives bearing vicinal tetrasubstituted stereocenters is reported. (DHQ)₂PHAL (4g) and quinine-derived squaramide (4d) were identified as efficient catalysts. Transformations of the Mannich-type reaction products highlight the utility of this synthetic strategy.

Synthesis of Lactams via Ir-Catalyzed C-H Amidation Involving Ir-Nitrene Intermediates

x-membered lactams were synthesized via either an amidation of sp³ C-H bonds or an electrophilic substitution of arenes via Ir-nitrene intermediates. With the employment of a readily available iridium catalyst in dichloromethane or hexafluoro-2-propanol, a wide range of lactams were synthesized in good to excellent yields with high selectivity.

Phosphine-catalyzed [3 + 2] annulation of 2-aminoacrylates with allenoates and mechanistic studies

A phosphine catalyzed formal [3 + 2] annulation was disclosed, affording 3-pyrrolines containing an amino quaternary stereogenic center in good to excellent yields. The catalytic mechanism was investigated by DFT and kinetic studies.

Asymmetric Synthesis of Enantioenriched 6-Hydroxyl Butyrolactams Promoted by N-Heterocyclic Carbene

Herein, an efficient route to synthesize 6-hydroxyl butyrolactams has been successfully developed via an N-heterocyclic carbene-catalyzed formal [3 + 2] annulation of bromoenals with α-amino ketones, followed by reduction. Remarkably, enantioenriched epi-neoclausenamide, which is one of the clausenamide derivatives, could be efficiently prepared by this strategy.

Palladium-Catalyzed [3 + 2]-C-C/N-C Bond-Forming Annulation

The synthesis of bi- and tricyclic structures incorporating pyrrolidone rings is disclosed, starting from resonance-stabilized acetamides and cyclic α,β-unsaturated-γ-oxycarbonyl derivatives. This process involves an intermolecular Tsuji-Trost allylation/intramolecular nitrogen 1,4-addition sequence. Crucial for the success of this bis-nucleophile/bis-electrophile [3 + 2] annulation is its well-defined step chronology in combination with the total chemoselectivity of the former step. When the newly formed annulation product carries a properly located o-haloaryl moiety at the nitrogen substituent, a further intramolecular keto α-arylation can join the cascade, thereby forming two new cycles and three new bonds in the same synthetic operation.

An uncommon multicomponent reaction involving nucleophilic heterocyclic carbenes: facile synthesis of fully substituted cyclopentanones

An unprecedented three component reaction involving arylidene oxazolone, enal and NHC, leading to the synthesis of fully substituted cyclopentanone derivatives with three contiguous stereocenters, is reported.

Competing mechanisms and origins of chemo- and stereo-selectivities of NHC-catalyzed reactions of enals with 2-aminoacrylates

A DFT study on competing mechanisms of NHC-catalyzed reactions of enals with 2-aminoacrylates has been performed for the first time.

Construction of spirothioureas having an amino quaternary stereogenic center via a [3 + 2] annulation of 3-isothiocyanato oxindoles with 2-aminoacrylates

A [3 + 2] annulation of 3-isothiocyanato oxindoles with 2-aminoacrylates was disclosed, affording the corresponding spirocyclic oxindoles containing a spirothiourea structure and an amino quaternary stereogenic center in good to excellent yields.