Direct (het)arylation of tetrahydroisoquinolines via a metal and oxidant free C(sp3)-H functionalization enabled three component reaction

Strategies Toward the Catalyst-Free α-C-H Functionalizations of Tertiary Amines

α-C-H functionalization of tertiary amines has been a highly studied field for the past two decades because several important nitrogen containing heterocycles or compounds can be synthesized through this strategy. Though transition metal catalysts and some metal-free catalysts are mainly used for these reactions, a few catalyst-free reactions have recently been efficiently performed. Catalyst-free reactions are cost-effective, less sensitive to air/moisture, easier to operate, have a simple purification process, and are relatively environment-friendly. In this article, we have summarized all the α-C-H functionalization reactions of tertiary amines performed without using any external catalysts. The content of this article will undoubtedly encourage readers to do more work in this area.

Oxidative α-Functionalization of 1,2,3,4-Tetrahydroisoquinolines Catalyzed by a Magnetically Recoverable Copper Nanocatalyst. Application in the Aza-Henry Reaction and the Synthesis of 3,4-Dihydroisoquinolones

The oxidative α-functionalization of 2-aryl-1,2,3,4-tetrahydroisoquinolines (THIQs) promoted by a versatile heterogeneous nanocatalyst consisting of copper nanoparticles immobilized on silica-coated maghemite (CuNPs/MagSilica) has been accomplished. The methodology was successfully applied in the cross-dehydrogenative coupling (CDC) reaction of N-aryl THIQs and other tertiary amines with nitromethane as a pro-nucleophile (aza-Henry reaction) and the α-oxidation of THIQs with O₂ as a green oxidant. Phosphite, alkyne, or indole derivatives were also shown to be suitable candidates for their use as pro-nucleophiles in the CDC reaction with THIQs. The catalyst, with very low copper loading (0.4-1.0 mol % Cu), could be easily recovered by means of an external magnet and reused in four cycles without significant loss of activity.

Condensation-Based Methods for the C-H Bond Functionalization of Amines

This review aims to provide a comprehensive overview of condensation-based methods for the C-H bond functionalization of amines that feature azomethine ylides as key intermediates. These transformations are typically redox-neutral and share common attributes with classic name reactions such as the Strecker, Mannich, Friedel-Crafts, Pictet-Spengler, and Kabachnik-Fields reaction, while incorporating a redox-isomerization step. This approach provides an ideal platform to rapidly transform simple starting materials into complex amines.

Synthesis of 1-benzylisoindoline and 1-benzyl-tetrahydroisoquinoline through nucleophilic addition of organozinc reagents to N,O-acetals

A new approach to access 1-benzylisoindoline and 1-benzyl-tetrahydroisoquinoline has been developed through nucleophilic addition of organozinc reagents to N,O-acetals. A number of substituted organozinc reagents were amenable for this transformation, and the desired products were obtained with excellent yields. Moreover, Sc(OTf)3 proved to be an effective catalyst for the formation of 1-benzylisoindoline and 1-benzyl-tetrahydroisoquinoline using such nucleophilic addition.

L-Proline-catalyzed regioselective C1 arylation of tetrahydroisoquinolines through a multicomponent reaction under solvent-free conditions

Here we disclose the C1 arylation of tetrahydroisoquinolines (THIQ) through regioselective C(sp3)-H functionalization using a multicomponent reaction. The reaction was performed by reacting THIQ, aldehydes and aminopyrazoles or indoles under neat conditions with l-proline as a catalyst. The regioselectivity of the products was confirmed by X-ray analysis and spectroscopic data. The formation of an azomethine ylide intermediate is crucial for obtaining the regioselectivity.

Diastereoselective and Reversed Regioselective Annulations of N-Alkyl Anilines to Julolidines and Lilolidines

A three-component annulation reaction of N-alkyl anilines, cyclic 1,3-dicarbonyl compounds, and aryl aldehydes to julolidines and lilolidines is reported. The 6π-electrocyclization enabled the annulation to proceed with reversed regioselectivity as compared with the annulation that occurs in the Povarov reaction. Both cyclic and acyclic N-alkyl anilines participated in the reaction to provide a wide range of julolidines and lilolidines as the single regio- and diastereoisomers in good to excellent yields.

Oxidative Dearomative Cross-Dehydrogenative Coupling of Indoles with Diverse C-H Nucleophiles: Efficient Approach to 2,2-Disubstituted Indolin-3-ones

The oxidative, dearomative cross-dehydrogenative coupling of indoles with various C-H nucleophiles is developed. This process features a broad substrate scope with respect to both indoles and nucleophiles, affording structurally diverse 2,2-disubstituted indolin-3-ones in high yields (up to 99%). The oxidative dimerization and trimerization of indoles has also been demonstrated under the same conditions.

KOtBu-promoted oxidative dimerizations of 2-methylquinolines to 2-alkenyl bisquinolines with molecular oxygen

KO^tBu-promoted oxidative dimerizations of 2-methylquinolines with molecular oxygen as the oxidant have been developed for the first time.