A Pd(II)-catalyzed intramolecular oxidative C-H/C-H cross-coupling has been developed for the direct construction of valuable polycyclic heteroarene scaffolds. From a retrosynthetic point of view, the strategic formation of a C-C bond via C(sp)-H/C(sp)-H dehydrogenative coupling across C3,N-linked biheterocyclic precursors may be useful in de novo syntheses of indole-derived natural products and pharmaceuticals. The reaction exhibited good functional group/heterocycle tolerance, and a proposed mechanism involving an azoylpalladium complex is also supported.

Indoline-fused polycycles were synthesized through a TFA-promoted intramolecular dearomative cyclization of indole-tethered pyrroles. Mechanistically, the strategic carbon-carbon bond formation is hypothesized to proceed via a Pictet-Spengler-type reaction wherein a reversal of conventional indole reactivity of tryptamine derivatives occurs. The synthetic versatility of this operationally simple, atom-economic approach is demonstrated in the preparation of the pyrido[1,2-a:3,4b']diindole core of natural product homofascaplysin C.

Zn(II)-catalyzed divergent synthesis of functionalized polycyclic indolines through formal [3 + 2] and [4 + 2] cycloadditions of indoles with 1,2-diaza-1,3-dienes (DDs) is reported. The nature and type of substituents of substrates are found to act as a chemical switch to trigger two distinct reaction pathways and to obtain two different types of products upon the influence of the same catalyst. The mechanism of both [4 + 2] and [3 + 2] cycloadditions was investigated and fully rationalized by density functional theory (DFT) calculations.

An umpolung α-(hetero)arylation strategy that involves the Michael-type reaction between electron-rich (hetero)aromatic substrates and azoalkenes is developed. The reaction proceeds under very mild conditions at room temperature and in the presence of inexpensive, nontoxic ZnCl 2 catalyst to provide access to otherwise inaccessible hydrazone structures. Subsequent hydrolysis of these latter to ketones as well as other valuable synthetic transformations to a variety of heterocyclic scaffolds demonstrate the usefulness of this protocol.T he direct installation of an aryl/heteroaryl substituent into the α-position of ketone has proven to be a transformation of great utility in pharmaceutical, agrochemical, and organic synthesis. 1 As result, there is an ever-growing number of methods reported in the literature, 2−4 most of them involving the addition of organometallic species or preformed enolates/ azaenolate to halide/pseudohalide. Despite significant advances in transition-metal-promoted carbon−carbon bond-forming reactions that have been made over the years, a general catalytic arylation/heteroarylation exploiting the C−H bonds of (hetero)aromatics, 5 the most abundant moiety in organic molecules, remains elusive. From the viewpoints of efficiency, sustainability, and atom-and step-economy, the replacement of C−X with C−H bonds that are unreactive under traditional approaches is therefore highly appealing.A polarity-reversed strategy 6 to introduce aryl substituents into the α-position of carbonyl compounds would employ unconventional reactivity patterns, such as azoalkenes 7−9 ("umpoled" carbonyl compounds) in the context of a Michael addition. With this objective, the transformation of a carbonyl

Substituted hydroxy-benzofurans are easily accessible by treatment of resorcinols and 1,2-diaza-1,3-dienes (DDs) under acidic conditions. The reaction happens through an uncommon Michael reaction between aromatic derivatives as aromatic C(sp 2 )−H nucleophiles and DDs as acceptors. Also, the behavior of different phenols and 2-naphthol was investigated.

A multicomponent reaction (MCR) strategy, alternative to the known cycloaddition reaction, towards variously substituted 1-amino-1H-imidazole-2(3H)-thione derivatives has been successfully developed. The novel approach involves α-halohydrazones whose azidation process followed by tandem Staudinger/aza-Wittig reaction with CS2 in a sequential MCR regioselectively leads to the target compounds avoiding the formation of the regioisomer iminothiazoline heterocycle. The approach can be applied to a range of differently substituted α-halohydrazones bearing also electron-withdrawing groups confirming the wide scope and the substituent tolerance of the process for the synthesis of the target compounds. Interestingly, the concurrent presence of reactive functionalities in the scaffolds so obtained ensures post-modifications in view of N-bridgeheaded heterobicyclic structures.

Herein, we report the successful syntheses of scarcely represented indole-based heterocycles which have a structural connection with biologically active natural-like molecules. The selective oxidation of indoline nucleus to indole, hydrolysis of ester and carbamoyl residues followed by decarboxylation with concomitant aromatization of the pyridazine ring starting from tetrahydro-1H-pyridazino[3,4-b]indole derivatives lead to fused indole-pyridazine compounds. On the other hand, non-fused indole-pyrazol-5-one scaffolds are easily prepared by subjecting the same C2,C3-fused indoline tetrahydropyridazines to treatment with trifluoroacetic acid (TFA). These methods feature mild conditions, easy operation, high yields in most cases avoiding the chromatographic purification, and broad substrate scope. Interestingly, the formation of indole linked pyrazol-5-one system serves as a good example of the application of the umpolung strategy in the synthesis of C3-alkylated indoles.

A Multicomponent Reaction (MCR) strategy, alternative to the known cycloaddition reaction, towards variously substituted 1-amino-1H-imidazole-2(3H)-thione derivatives has been successfully developed. The novel approach involves α-halohydrazones whose azidation process followed by tandem Staudinger/aza-Wittig reaction with CS2 in a sequential MCR regioselectively leads to the target compounds avoiding the formation of the regioisomer iminothiazoline heterocycle. The approach can be applied to a range of differently substituted α-halohydrazones bearing also electron-withdrawing groups confirming the wide scope and the substituent tolerance of the process for the synthesis of the target compounds. Interestingly, the concurrent presence of reactive functionalities in the scaffolds so obtained, ensures postmodifications in view of N-bridgedheaded heterobicyclic structures.