Mono and di ortho-C-H acetoxylation of 2-aryloxyquinoline-3-carbaldehydes.

2-Aryloxyquinolines are well known for various biological activities. In this report, we have developed a novel protocol for introducing an acetoxy functional group on the aryl sp2 carbon of 2-aryloxyquinoline-3-carbaldehyde using a palladium catalyst for the first time. Interestingly, this C-H acetoxylation reaction is highly chemo- and site-selective. By modifying the reaction conditions, mono or di ortho-C-H acetoxylation products have been synthesized selectively with good yields and with good functional group tolerance.

Distal meta-C-H functionalization of α-substituted cinnamates.

Development of a novel strategy for the palladium-catalyzed selective meta-C-H activation of α-substituted cinnamates and their heterocyclic analogues with various alkenes using nitrile as a directing group (DG) has been described. Importantly, we introduced naphthoquinone, benzoquinones, maleimides and sulfolene as coupling partners in the meta-C-H activation reaction for the first time. Notably, allylation, acetoxylation and cyanation were also achieved through distal meta-C-H functionalization. This novel protocol also includes the coupling of various olefin-tethered bioactive molecules with high selectivity.

Palladium-catalyzed remote meta-C-H olefination of cinnamates.

The palladium-catalyzed remote meta-C-H olefination of geometrically challenging substituted cinnamates using a nitrile directing group derived from 2-cyanobenzoic acid has been described. This new protocol is applicable to various olefin coupling partners and provides the corresponding meta-olefinated products in very good yields and with high selectivity. In addition, using this methodology, a variety of acrylates with tethered bioactive molecules, such as naphthoquinone, methyl salicylate, paracetamol, thymol, sesamol, chalcone, naproxen, cholesterol and estrone, have been coupled to produce the desired meta-olefinated products.

Ester-directed orthogonal dual C-H activation and ortho aryl C-H alkenylation via distal weak coordination.

An unprecedented orthogonal cross-coupling between aromatic C(sp2) and aliphatic olefinic C(sp2) carbons of two same molecules via dual C-H bond activation in an intermolecular fashion has been developed using a distal ester-directing group. This new coupling reaction led to the synthesis of the highly functionalized 1,3-diaryl molecular architecture in very good yields and with high chemo- and regioselectivities. In addition, using ester as the distal directing group, ortho C-H olefination of α-methyl aryl acrylates and cinnamic esters with various alkenes has been achieved in very good yields and with a wide range of substrate scope.

Azomethine ylide cycloaddition of 1,3-dienyl esters: highly regio- and diastereoselective synthesis of functionalized pyrrolidinochromenes.

An efficient protocol for the synthesis of tricyclic pyrrolidinochromenes has been developed via an intramolecular 1,3-dipolar cycloaddition of azomethine ylides generated in situ from 1,3-dienyl ester tethered O-hydroxyarylaldehyde and glycine esters. The reaction is highly regio- and diastereoselective in nature and provided the potentially bioactive pyrrolidine fused tricyclic cycloadducts in excellent yields with wide substrate scope. Interestingly this reaction constructs two rings and four contiguous stereogenic centers in which one of them is an all carbon quaternary center in a unique fashion.

Ruthenium-catalyzed, site-selective C-H activation: access to C5-substituted azaflavanone.

A site-selective ruthenium-catalyzed keto group assisted C-H bond activation of 2-aryl tetrahydroquinoline (azaflavanone) derivatives has been achieved with a variety of alkenes for the first time. A wide range of substrates was utilized for the synthesis of a wide variety of alkenylated azaflavanones. This simple and efficient protocol provides the C5-substituted azaflavanone derivatives in high yields with a broad range of functional group tolerance. Further, the C5-alkenylated products were converted into substituted 2-aryl quinoline derivatives in good yields.

Solvent and catalyst free ring expansion of indoles: a simple synthesis of highly functionalized benzazepines.

Highly functionalized benzazepines have been synthesized by using various substituted indoles and dialkylacetylene dicarboxylates under thermal and open air conditions. The reaction was carried out in a solvent and under catalyst free conditions and the products are formed in very good yields. The reaction proceeds in a concerted fashion thus providing potentially bioactive benzazepines by ring expansion of a five-membered indole ring. It is also described that the ring contraction of seven-membered benzazepines in the presence of KOtBu base at room temperature smoothly afforded the corresponding 3-alkenylated indole derivatives in very good yields.