Utilization of DMSO as a solvent-cum-reactant: synthesis of fused 2-aryl-4-methylquinolines.

Herein, we disclose the synthesis of a variety of disubstituted fused quinoline, such as 4-methyl-2-arylbenzo[h]quinolines (3a-j), 1-methyl-3-arylbenzo[f]quinolines (3k-r), 1-methyl-3-arylnaphtho[2,3-f]quinolines (3s-x), and 2-aryl-5,7-dimethoxy-4-methylquinolines (4a-c), derivatives from the reaction of an aryl aldehyde with 1-naphthylamine (1a), 2-naphthylamine (1b), 2-aminoanthracene (1c) and 3,5-dimethoxyaniline (1d), respectively, at 80 °C in the presence of 30 mol% (±)-10-camphorsulfonic acid ((±)-CSA) using DMSO as the solvent-cum-reactant. DMSO molecules regioselectively incorporate three carbon atoms into the target molecule in this distinct reaction. The other advantages of the present protocol are that it can be performed under mild reaction conditions and does not require metal catalysts, additional additives or oxidants.

One-Step Synthesis of 7-Bromobenzo[c]chromeno[4,3,2-gh]phenanthridines through a Sequential Bromination/Cyclization/Aromatization Reaction Using N-Bromosuccinimide (NBS).

Herein, metal- and oxidant-free synthesis of 7-bromobenzo[c]chromeno[4,3,2-gh]phenanthridines is reported using N-bromosuccinimide. Sequential regioselective bromination, intramolecular ring cyclization, and aromatization reactions occur in a single step through a successive radical-catalyzed pathway. The mechanistic pathway for the cyclization is supported by a DFT study. Selective bromination in the fully aromatic skeleton is accomplished without involving additional aromatic electrophilic ring bromination. As a synthetic application, the Suzuki coupling reaction of compound 5a with boronic acid is reported to get compound 8a. Aggregation-induced emission of one of the synthesized compounds (5h) is also investigated in THF/hexane solvent along with concentration-dependent emission spectroscopy.

Regioselective synthetic approach for key precursors of 6-arylbenzo[c]phenanthridin-10-ol derivatives: a useful compound for selective chromogenic recognition of fluoride.

A regioselective synthetic strategy for 6-aryl-8,9-dihydrobenzo[c]phenanthridine-10(7H)-ones (4) is accomplished using a one-pot four-component reaction by fine-tuning the reaction temperature. DMSO is excellently used as a reactant-cum-solvent to introduce a carbonyl functionality regioselectively at the C-10 position of the benzophenanthridine backbone, via an MCR, which is unknown yet. The elegant features of this strategy are the formation of two CC, one CN, and one CO bonds in a single step, without using a base and an activator for the oxygenation process. Then, a few compounds (4) are easily aromatised to achieve 6-arylbenzo[c]phenanthridin-10-ol derivatives (7) using I2/DMSO at 100 °C. Nay, a dangling hydroxyl group in 4s, 4u, 4x, and 4z helped them to be employed as promising 'naked eye' colorimetric chemosensors for fluoride with limits of detection of 0.65, 0.60, 0.34, and 2.2 ppm, respectively. Moreover, the reversibility of the chemosensors makes them suitable for combinatorial INHIBIT logic gate formulation. The compounds have also been employed for solid-state F- detection via the spot TLC test.

DMSO-assisted environmentally benign synthesis of benzo[c]-chromeno[4,3,2-gh]phenanthridines by remote oxidative hetero cross-coupling cyclization and aromatization reaction.

An unprecedented metal-free and catalyst-free synthesis of benzo[c]chromeno[4,3,2-gh]phenanthridine derivatives, a class of 1,6-diheterophenalenoid heterocycle, is reported for the first time. The oxidative cross-coupling reaction for the remote cyclization is achieved through the in situ generated o-quinone methide intermediate followed by an electrocyclic ring closure reaction. The aromatization of the cyclohexane ring is achieved by sequential H shift, hydroxylation, and elimination reaction. DMSO-assisted concomitant cyclization and aromatization reactions are also disclosed for the first time.

Reactivity switch-over of 4-hydroxydithiocoumarins under various conditions and their application in organic synthesis.

4-Hydroxydithiocoumarin is a valuable organic precursor to architect important heterocycles. The three different reactive nucleophilic sites in 4-hydroxydithiocoumarins display intriguing regioselectivity in their reaction towards various electrophiles. Previously, 4-hydroxydithiocoumarins have been used in the synthesis of heterocycles using Claisen and thio-Claisen reactions. Hetero-Diels-Alder reactions involving 4-hydroxydithiocoumarins have proven to be very convenient in assembling complex molecular organic frameworks from readily available feedstocks. Development of multicomponent reactions employing 4-hydroxydithiocoumarins has given rise to several important reaction protocols to access polycyclic compounds. Recently, this moiety has been used in forging some unusual S-S, S-N and S-O bonds under oxidative conditions which further explores its hidden reactivity in organic synthesis. Besides that, hydrothiolation of various alkynes and alkenes using 4-hydroxydithiocoumarins has led to the synthesis of some potential lead molecules. This mini-review provides an account of the reactivity pattern of 4-hydroxydithiocoumarins and their strategic applications in various reactions for the synthesis of several heterocycles and other important organic syntheses.

Synthesis of vinyl sulfides and thioethers via a hydrothiolation reaction of 4-hydroxydithiocoumarins and arylacetylenes/styrenes.

The synthesis of vinyl sulfides (3a-m) and thioethers (7a-k), exclusive Markovnikov products, is reported by a copper(I) iodide catalyzed regioselective hydrothiolation reaction of terminal alkynes/alkenes and 4-hydroxydithiocoumarins. However, anti-Markovnikov hydrothiolation products (5a-f) were obtained in the case of 2-ethynylpyridine, with exclusive Z selectivity in good yields. The important aspects of this protocol are the absence of expensive metal complexes and additives to act as ligands, mild reaction conditions, high regioselectivity, good yields, and shorter reaction times.

Synthesis of biologically active fused 1,4-oxathiin derivatives from 4-hydroxydithiocoumarins, arylacetylenes and dimethyl sulfoxide by Cu(i)-catalyzed C-H functionalization and cross-dehydrogenative C-S coupling reactions.

The hitherto unreported 2-aryl-10H-thiochromeno[3,2-b][1,4]oxathiin-10-one derivatives are obtained in a single pot from 4-hydroxydithiocoumarins, arylacetylenes and dimethyl sulfoxide in the presence of 10 mol% CuI and K2CO3 in an oil bath at 70 °C. The novelties of the present protocol are (i) selective C-H functionalization at the C-3 position of 4-hydroxydithiocoumarin, (ii) regioselective hydrothiolation with arylacetylenes and (iii) concomitant cyclisation. The major advantages are mild reaction conditions, broad substrate scope and good yield. Among the synthesized compounds, the following five compounds 3aa, 3bd, 3ec, 3fa, and 3fd showed anticancer activity against a human breast cancer cell line (MCF-7) and a cervical cancer cell line (HeLa).