KI-Catalyzed C(sp3)-H Amination and Acyloxylation of Indolin-3-ones Using Air as the Oxidant

We have developed an efficient and green strategy for the synthesis of C2-amino indolin-3-ones and C2-acyloxy indolin-3-ones via KI-catalyzed C(sp3)-H amination and acyloxylation of indolin-3-ones using air as the oxidant. The reaction provides straightforward access to 2-substituted indolin-3-ones by the direct functionalization of indolin-3-ones at the C2 position under mild conditions. Moreover, the conditions enable direct functionalization of a range of complex pharmaceuticals, providing attractive products for medicinal chemistry programs.

A novel quinoline-based NNN-pincer Cu(II) complex as a superior catalyst for oxidative esterification of allylic C(sp3)-H bonds

We report for the first time that the quinoline-based NNN-pincer Cu(II) complex acts as an air stable superior catalyst for the oxidative cross-coupling of the allyl sp³ C-H bond with an acid for the synthesis of allyl esters in a homogeneous system at ambient temperature. The synthesized catalyst, 1, has been well characterized by various analytical techniques (HRMS, single crystal X-ray diffraction, CV, EPR, UV-vis spectroscopy) and showed excellent catalytic activity for the oxidative esterification of allylic C(sp³)-H bonds at 40 °C within a very short period of time (1 h) using only 1 mol% of the catalyst. A wide variety of aromatic allylic esters were synthesized in moderate to good yields, which could be extended to aliphatic allyl esters as well.

Copper Porphyrin-catalyzed C(sp3)-H Activation via Cross Dehydrogenative Coupling: Facile Transformation of Aldehydes to Esters

Copper porphyrin-catalyzed alkane C−H bond functionalization with aldehydes via cross dehydrogenative coupling (CDC) using DTBP oxidant has been firstly described in non-solvents or non-additives system. Different aryl/heteroaryl-carboxilic esters were obtained in good to excellent yields depending on the aldehyde derivatives. This CDC reaction catalyzed by copper porphyrin has the advantages of shorter reaction time, lower reaction temperature and catalyst loading as well as the aerobic reaction atmosphere.

From methylarenes to Esters: Efficient oxidative Csp3-H activation promoted by CuO decorated magnetic reduced graphene oxide

Magnetic reduced graphene oxide supported CuO (rGO/Fe3O4-CuO) as the heterogeneous catalyst in cross dehydrogenative coupling (CDC) reactions has been demonstrated for the synthesis of esters using methyl aromatics, aldehydes/benzyl alcohols...

Direct access to α-acyloxycarbonyl compounds and esters via oxidative esterification of aldehydes under visible light

An efficient synthesis of α-acyloxycarbonyl compounds and esters from aldehydes and α-bromocarbonyl compounds/benzyl bromide derivatives via photoredox catalysis has been developed.

An Electrochemical Method for Carboxylic Ester Synthesis from N-Alkoxyamides

An electrochemical method for the synthesis of carboxylic as well as hindered esters from N-alkoxyamides has been reported. The electrochemical reaction proceeds through constant current electrolysis (CCE) by taking advantage of the dual role of n-Bu₄NI (TBAI) as the redox catalyst as well as the supporting electrolyte. Besides providing mild reaction conditions, the present protocol is free from external oxidants and conducting salts, thereby generating nitrogen as the nonhazardous side product. Additionally, the developed procedure is highly advantageous due to its short reaction time, wide substrate scope, and gram-scale synthesis.

Visible-Light Mediated Oxidative C-H/N-H Cross-Coupling between Tetrahydrofuran and Azoles Using Air

Tetrahydrofuran is a privileged structural moiety in many important organic compounds. In this work, we have developed a simple and mild catalytic oxidative amination of tetrahydrofuran mediated by visible-light catalysis. The C(sp3)-H bond of tetrahydrofuran was activated using molecular oxygen as a benign oxidant. Besides, a variety of azoles could be tolerated, providing a green route for N-substituted azoles.

Direct intramolecular amination of tryptophan esters to prepare pyrrolo[2,3-b]indoles

A metal-free iodine-catalyzed intramolecular amination has been developed for the practical synthesis of pyrrolo[2,3-b]indoles from readily available tryptophan esters. The transformation has been applied to a wide array of substrates and can be performed on gram scale under very mild conditions.

Regio- and stereoselective syntheses of allylic thioethers under metal free conditions

A metal-free, regio and stereoselective synthesis of allylic thioethers using densely functionalized allyl iodides and aryl/alkyl disulfides as coupling partners, provided the resulting allyl aryl thioethers in 62–92% isolated yields is described.

Synthesis of benzyl esters from the commercially available alcohols catalyzed by TBAI via C(sp3)–H bond functionalization

The direct esterification of alcohol catalyzed by TBAI via C(sp³)–H bond functionalization was achieved under mild and clean conditions with good to excellent yields.

Catalyst-Free sp3 C-H Acyloxylation: Regioselective Synthesis of 1-Acyloxy Derivatives of the Natural Product Tanshinone IIA

Tanshinone IIA is a valuable bioactive natural product isolated from the well-known Chinese herb Danshen. Structural manipulation of the A-ring of tanshinone IIA is rather limited. In this study, a substrate tautomerization-induced catalyst-free benzylic sp³ C-H acyloxylation approach is reported that allows the direct introduction of various acyloxy groups at the A-ring benzylic methylene of various tanshinone IIA substrates, thus avoiding the use of expensive transition metal catalysts and the production of harmful byproducts. This approach features a unique acid-induced reversible enolization/oxa-conjugate addition process followed by oxidation to exclusively give a series of diverse 1-acyloxylated derivatives under simple conditions in a regioselective manner. Compared with the literature procedures, this protocol demonstrates a higher efficiency, a more robust functional-group tolerance, atom economy, and lower cost.

Efficient photolytic C-H bond functionalization of alkylbenzene with hypervalent iodine(iii) reagent

A practical approach to radical C-H bond functionalization by the photolysis of a hypervalent iodine(iii) reagent is presented. The photolysis of [bis(trifluoroacetoxy)iodo]benzene (PIFA) leads to the generation of trifluoroacetoxy radicals, which allows the smooth transformation of various alkylbenzenes to the corresponding benzyl ester compounds under mild reaction conditions.

In Situ Generated HypoIodite Activator for the C2 Sulfonylation of Heteroaromatic N-oxides

A mild approach for direct C2 sulfonylation of heteroaromatic N-oxides with sulfonyl hydrazides affording 2-sulfonyl quinolines/pyridines has been developed. A variety of heteroaromatic N-oxides and sulfonyl hydrazides participate effectively in this transformation which uses hypoiodites (generated in situ from NaI and TBHP) as a means of substrate activators. In this reaction, the N-oxide plays a dual role, acting as a traceless directing group as well as a source of oxygen atom.

Direct difunctionalization of activated alkynes via domino oxidative benzylation/1,4-aryl migration/decarboxylation reactions under metal-free conditions

The oxidative difunctionalization of aryl alkynoatesviaa tandem oxidative benzylation/1,4-aryl migration/decarboxylation to trisubstituted alkenes was developed under metal-free conditions.

NBS/DBU mediated one-pot synthesis of α-acyloxyketones from benzylic secondary alcohols and carboxylic acids

A simple and efficient NBS/DBU-mediated one-pot procedure has been developed for the synthesis of α-acyloxyketones from benzylic secondary alcohols and carboxylic acids.

Synthesis of esters via sp3 C–H functionalisation

This review describes various methods for the synthesis of eleven classes of esters involving sp³ C–H functionalisation.