Visible Light-Mediated Heterodifunctionalization of Alkynylazobenzenes for 2H-Indazole Synthesis

We disclose the heterodifunctionalization of alkynylazobenzenes promoted exclusively by visible light in the absence of any transition metal and/or photocatalyst. This reaction features excellent regioselectivity on a broad variety of substrates with perfect atom economy. Alcohols, carboxylic acids, thiols, amides, heterocycles, and even water are suitable substrates for the promotion of the oxyamination, sulfenoamination, and diamination reactions. In this manner, biologically active indazole scaffolds can be rapidly assembled from alkyne feedstocks.

Recent Applications on Dual-Catalysis for C–C and C–X Cross-Coupling Reactions

Coupling reactions stand amid the most significant reactions in synthetic organic chemistry. Of late, these coupling strategies are being viewed as a versatile synthetic tool for a wide range of organic transformations in many sectors of chemistry, ranging from indispensable synthetic scaffolds and natural products of biological significance to novel organic materials. Further, the use of dual-catalysis in accomplishing various interesting cross-coupling transformations is an emerging field in synthetic organic chemistry, owing to their high catalytic performance rather than the use of a single catalyst. In recent years, synthetic organic chemists have given considerable attention to hetero-dual catalysis; wherein these catalytic systems have been employed for the construction of versatile carbon–carbon [C(sp 3)–C(sp 3), C(sp 3)–C(sp 2), C(sp 2)–C(sp 2)] and carbon–heteroatom (C–N, C–O, C–P, C–S) bonds. Therefore, in this mini-review, we are emphasizing recently developed various cross-coupling reactions catalysed by transition-metal dual-catalysis (i.e., using palladium and copper catalysts, but omitting the reports on photoredox/metal catalysis).

1 Introduction

2 Cu/Pd-Catalysed Bond Formation

2.1 Pd/Cu-Catalysed C(sp 3)–C(sp 2) Bond Formation

2.2 Pd/Cu-Catalysed C(sp 2)–C(sp 2) Bond Formation

2.3 Pd/Cu-Catalysed C(sp)–C(sp 2) Bond Formation

2.4 Pd/Cu-Catalysed C(sp 3)–C(sp 3) Bond Formation

2.5 Pd/Cu-Catalysed C–X (X = B, N, P, S, Si) Bond Formation

3 Conclusion

Access to Phosphine-Containing Quinazolinones Enabled by Photo-Induced Radical Phosphorylation/Cyclization of Unactivated Alkenes

A mild and facile photo-induced cascade radical addition/cyclization of unactivated alkenes has been reported, through which a variety of biologically valuable phosphine-containing quinazolinones could be obtained in moderate to good yields. The protocol was characterized by mild conditions, broad substrate scope, and high atomic economy.

Dirhodium(ii)-catalysed cycloisomerization of azaenyne: rapid assembly of centrally and axially chiral isoindazole frameworks

Described herein is a dirhodium(ii)-catalyzed asymmetric cycloisomerization reaction of azaenyne through a cap-tether synergistic modulation strategy, which represents the first catalytic asymmetric cycloisomerization of azaenyne. This reaction is highly challenging because of its inherent strong background reaction leading to racemate formation and the high capability of coordination of the nitrogen atom resulting in catalyst deactivation. Varieties of centrally chiral isoindazole derivatives could be prepared in up to 99 : 1 d.r., 99 : 1 er and 99% yield and diverse enantiomerically enriched atropisomers bearing two five-membered heteroaryls have been accessed by using an oxidative central-to-axial chirality transfer strategy. The tethered nitrogen atom incorporated into the starting materials enabled easy late-modifications of the centrally and axially chiral products via C–H functionalizations, which further demonstrated the appealing synthetic utilities of this powerful asymmetric cyclization.

Rh(ii)-catalyzed asymmetric cycloisomerization of azaenyne through a cap-tether synergistic modulation strategy was described. Diverse centrally and axially chiral isoindazoles were prepared and directed C–H late-stage modifications were developed.

Visible-light-facilitated P-center radical addition to C[double bond, length as m-dash]X (X = C, N) bonds results in cyclizations

Visible-light-facilitated phosphorus radical reactions have been developed as a powerful and sustainable tool for the synthesis of various organophosphorus compounds. In general, these reactions require stoichiometric amounts of oxidants, and reductants, bases, and radical initiators, leading to uneconomical and complicated processes. Progress has been made over the past few years toward using reactions that proceed under eco-benign and mild reaction conditions. Furthermore, these reactions have broad functional group tolerance, with some facile and economical pathways. Herein, we summarize the discoveries and achievements pertaining to C-P bond formation through a visible light photocatalysis procedure with high atom economy, made by our group and other research groups. It was established that greener and more environmentally friendly approaches do not require an additional oxidant or base. Moreover, we have designed and synthesized a new type of P-radical precursor, which can take part in reactions without the requirement for any additional bases, oxidants, and additives. This breakthrough, pertaining to novel visible-light-induced transformations, will be discussed and a plausible mechanism is proposed, based on corresponding experiments and the literature.

Controllable chemoselectivity in the reaction of 2H-indazoles with alcohols under visible-light irradiation: synthesis of C3-alkoxylated 2H-indazoles and ortho-alkoxycarbonylated azobenzenes

A high chemoselectivity in the visible-light-induced reaction of 2H-indazoles with alcohols controlled by the reaction atmosphere was achieved, providing C3-alkoxylated 2H-indazoles and ortho-alkoxycarbonylated azobenzenes.

Recent Advances in Metal-Catalyzed Heterocyclic C-P Bond Formation

The phosphorus-containing heterocycles are an important class of compounds in organic chemistry. Because of their potential application in many fields, especially, the synthetic pesticides, medicine and catalyst, the phosphorus-containing heterocycles have attracted continuous attention from organic synthesis scientists. The development of efficient and low-cost catalytic systems is of great interest for the construction of heterocycles C-P bond. Usually, the phosphorus-containing heterocycles is prepared via direct carbon-hydrogen (C-H) bond activation or pre-functionalized of heterocycles with phosphorus-hydrogen (P-H) bond of phosphorus compounds reaction by metal-catalyzed. This review summarizes recent progress in the heterocycles C-P bond formation reactions by metal-catalyzed, which mainly focus on the discussion of the reaction mechanism. It aims to provide efficient methods for the future synthesis and application in this field.

Recent Advances in Indazole-Containing Derivatives: Synthesis and Biological Perspectives

Indazole-containing derivatives represent one of the most important heterocycles in drug molecules. Diversely substituted indazole derivatives bear a variety of functional groups and display versatile biological activities; hence, they have gained considerable attention in the field of medicinal chemistry. This review aims to summarize the recent advances in various methods for the synthesis of indazole derivatives. The current developments in the biological activities of indazole-based compounds are also presented.

Copper-catalyzed decarboxylative cyclization via tandem C–P and C–N bond formation: access to 2-phosphorylmethyl indoles

A copper-catalyzed decarboxylative cyclization of ethynyl benzoxazinanones with P(O)H compounds has been developed for the synthesis of 2-phosphorylmethyl indoles.