Anugula Nagaraju

ortho-Quinone methide (o-QM): a highly reactive, ephemeral and versatile intermediate in organic synthesis

Since its first observation in 1907, ortho-quinone methide (o-QM) has occupied a strategic place within the framework of reactive intermediates in organic synthesis. In recent years, o-QM has enhanced its importance as a versatile reactive intermediate, and its applications in organic synthesis, material chemistry, fine chemicals, and pharmaceuticals are increasing rapidly. This critical review summarizes the key concepts behind o-QMs and provides an overview of current applications in organic synthesis to provide an appropriate background for synthetic, medicinal and combinatorial developments. This review covers the literature from its origin to the mid of 2014 (112 references).

4-Dimethylamino pyridine-promoted one-pot three-component regioselective synthesis of highly functionalized 4H-thiopyrans via heteroannulation of β-oxodithioesters.

A highly convergent and regioselective heteroannulation protocol for the synthesis of hitherto unreported highly substituted 2-amino-4-(aryl/alkyl)-5-(aroyl/heteroaroyl)-3-(cyano/carboalkoxy)-6-methylthio-4H-thiopyran derivatives has been developed. This one-pot three-component domino coupling of β-oxodithioesters, aldehydes, and malononitrile/ethyl or methyl cyanoacetate is promoted by 4-dimethylamino pyridine (DMAP) in solvent (dichloromethane (DCM)) as well as under solvent-free conditions. Systematic optimization of reaction parameters identified that the three-component coupling (3CC) protocol is tolerant to a wide array of functionality providing densely functionalized 4H-thiopyrans in excellent yields. The merit of this cascade Knoevenagel condensation/Michael addition/cyclization sequence is highlighted by its high atom-economy, excellent yields, and efficiency of producing three new bonds (two C-C and one C-S) and one stereocenter in a single operation.

Catalyst-free one-pot four-component domino reactions in water–PEG-400: highly efficient and convergent approach to thiazoloquinoline scaffolds

A cost-effective and eco-friendly straightforward synthesis of highly diversified thiazoloquinoline scaffolds is successfully achieved via one-pot four-component cascade reaction utilizing α-enolic dithioesters, cysteamine, aldehydes, and cyclic 1,3-diketones in water–PEG-400. The new efficient domino protocol generates two rings by the concomitant formation of C–C (two), C–N (two), and C–S multiple bonds presumably involving a sequence of N,S-acetal formation, Knoevenagel reaction, aza–ene reaction, imine–enamine/keto–enol tautomerization, and N-cyclization as key steps. The merit of this protocol is highlighted by its easily available and economical starting materials, operational simplicity, efficient utilization of all the reactants, clean reaction profile, simple workup procedure, and tolerance of a wide variety of functional groups.

Eco-efficient, regioselective and rapid access to 4,5-disubstituted 1,2,3-thiadiazoles via [3 + 2] cycloaddition of α-enolicdithioesters with tosyl azide under solvent-free conditions

An efficient, sustainable, and regioselective one-pot synthesis of hitherto unreported 4-aroyl/hetaroyl/alkanoyl-5-alkyl/allyl/benzylsulfanyl-1,2,3-thiadiazoles has been achieved by [3 + 2] cycloaddition of α-enolicdithioesters with tosyl azide through cascade 1–2 (S–N) and 3–4 (C–N) bond connections involving Wolff-type heterocyclization. Optimally, the reactions are very fast and completed within 2–15 minutes, when a mixture of α-enolicdithioester and tosyl azide was stirred at 0 °C in the presence of Et3N under solvent-free conditions. Furthermore, no co-catalyst or activator is necessary. The eco-compatibility, mild conditions, excellent yields, easy purification, and avoidance of expensive/toxic reagents are advantages of this protocol to access this medicinally privileged substructure.

DMAP mediated one-pot domino thienannulation: a versatile, regioselective and green mechanochemical route to naphtho[2,3-b]thiophenes

Solvent-free mechanochemical route to naphtho[2,3-b]thiophenes via [3 + 2] oxidative heteroannulation of α-enolicdithioesters and β-oxothioamides with 1,4-naphthoquinone has been achieved at room temperature.

DMAP-promoted domino annulation of β-ketothioamides with internal alkynes: a highly regioselective access to functionalized 1,3-thiazolidin-4-ones at room temperature

DMAP-mediated rapid and efficient one-pot regioselective access to functionalized 1,3-thiazolidin-4-ones via annulation of β-ketothioamides with internal alkynes has been achieved under mild reaction conditions. The merit of this straightforward domino protocol is highlighted by its operational simplicity, short reaction time, tolerance of a large variety of functional groups, and efficiency of producing two new bonds (C–S and C–N) and one thiazolidine ring.