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Until now, a myriad of effective approaches have emerged for the functionalization of N -heteroaryl C-H bonds. In contrast, dearomatization and construction of fused heterocycles from activated heteroarenes is still a subject to explore. In this work, we present a refined approach for both dearomatization of N -heteroarenes and the synthesis of fused heterocycles from activated heteroarenes ruthenium catalysis using paraformaldehyde along with additive and base. Notably, quinolinium salts with a hydrogen at the C-4 position yield a methoxymethyl-substituted fused cyclic product through the Thorpe Ingold effect. An innovative aspect of this research is the dual functionality of paraformaldehyde as both a hydride donor and electrophile, utilizing readily available feedstock chemicals. A broad range of electron withdrawing and donating substituents was tolerable under standardized reaction conditions.

A divergent formal synthesis of polyhydroxylated macrocyclic lactone (+)-aspicillin and polyene bioactive natural product β-parinaric acid and the total synthesis of non-terpenoid metabolite isolaurepan have been achieved using a ruthenium-catalyzed stereo- and chemoselective oxidative coupling reaction of easily accessible vinyl ketones and acrylates. The crucial transformation involves the efficient synthesis and functionalization of stereodefined ( E,E )-1,6-dioxo-2,4-dienes using simple reaction protocols, which enabled straightforward access to a diverse range of bioactive natural products.

Herein, we report the asymmetric Ru/cinchonine dual catalysis that provides straightforward access to enantioselective synthesis of C-3 substituted phthalides via tandem C-H activation/Michael addition cascade. The use of readily accessible and less expensive [RuCl 2 (p-cym)] 2 and cinchonine catalyst for the one-pot assembly of chiral phthalides greatly overcomes the present trend of using highly sophisticated catalysts. The developed method provides access to both enantiomers of a product using pseudoenantiomeric cinchona alkaloids as catalysts streamlining the synthesis of phthalide in both the optically active forms.

An oxidative cross-coupling reaction between activated olefins and vinyl boronate derivatives has been developed for the highly stereoselective construction of synthetically useful ( E , E )-1,3-dienes. The highlight of this reaction is that exclusive stereoselectivity (only E , E -isomer) was achieved from a base-free, ligand-free, and mild catalytic condition with a less expensive [RuCl 2 ( p -cymene)] 2 catalyst.

A weakly coordinating, carbonyl-assisted C-H activation of aromatic systems with α,β-unsaturated ketone and subsequent aldol condensation has been developed using a Cp*Co(CO)I 2 catalyst. The developed method is the first example of indene synthesis by cobalt-catalyzed C-H activation. In addition, the reaction requires mild reaction conditions and easily accessible starting materials, and it shows excellent functional group compatibility.

A full account on the first total synthesis of a chroman meroterpenoid, (-)-phomoarcherin C, has been described. Key synthetic transformations include phenyl boronic acid-mediated 6π-electrocyclization reaction, a stereospecific hydrogenation driven by thermodynamic conformational stability of the product, and regioselective formylation. The strategy employed is considerably short, is atom-economical, and can open the doors to provide access to various other natural products of the same kind.

Total synthesis of (±)-adunctin B, a natural product isolated from Piper aduncum (Piperaceae), has been achieved using two different strategies, in seven and three steps. The efficient approach features highly atom economical and diastereoselective Friedel-Crafts acylation, alkylation reaction and palladium catalyzed Wacker type oxidative cyclization.

An intramolecular FeCl3-catalyzed Michael addition reaction of styrene, a poor nucleophile, onto α,β-unsaturated ketones was developed for the synthesis of highly substituted indene derivatives. The method was further applied to the total synthesis of the sesquiterpene natural products (±)-jungianol and 1-epi-jungianol.

A one-step protocol has been developed for the enantioselective synthesis of hexahydrodibenzofuran derivatives using a modified Friedel-Crafts reaction. The developed method was applied to the synthesis of a series of natural products including (+)-hostmanin A, (+)-methyllinderatin, and (-)-linderol A. The synthetic and spectroscopic data investigations led to the structural reassignment of natural product adunctin E, which was further confirmed by single-crystal X-ray analysis.

Dimeric indole alkaloids represent a structurally unique class of natural products having interesting biological activities. Recently, we reported the first total synthesis of flinderoles B and C, structurally unique and potent antimalarial natural products. Central to the design of the approach and by virtue of a one-pot, acid-catalyzed dimerization reaction, the route also provided total synthesis of the borreverine class of natural products. This full account details the progress of efforts that culminated in the protecting-group-free, six-step total synthesis of all of the flindersia alkaloids: dimethylisoborreverine, isoborreverine, flinderoles A-C, and their analogues. A biomimetic approach featuring a scalable and catalytic formal [3 + 2] cycloaddition and Diels-Alder reaction is outlined in detail. On the basis of the experimental observations, a detailed mechanism has been proposed for the dimerization of tertiary alcohol 28.