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Bicyclo[1.1.1]pentane (BCP) replacement as a bioisostere in drug molecules has an influence on their permeability, aqueous solubility and in vitro metabolic stability. Thus, the chemical installation of the BCP unit into a chemical entity remains a significant challenge from a synthetic point of view. Here, we have presented a new approach for the installation of the BCP unit on the xanthate moiety by means of a radical exchange process.

An efficient copper‐catalyzed protocol has been developed for the synthesis of carbamates from dialkylformamides and phenols possessing directing groups such as benzothiazole, quinoline and formyl at the ortho‐position. In this chelation assisted approach, C-O bond formation takes place via a Cross Dehydrogenative Coupling (CDC) between the formyl C-H of dialkylformamide and phenolic O-H in the presence of copper(II)acetate/aqueous tert‐butyl hydroperoxide. Under identical reaction conditions, salicylic acid derivatives underwent amidation with the carboxylic group rather than formamidation of the phenolic OH. The use of a cheap and environmentally benign catalyst along with the tolerance of a wide range of functional groups makes this an easy, phosgene‐free route to carbamates.

A unique copper-catalyzed cross-dehydro- genative coupling (CDC) of thiols and alkylbenzenes has been developed for the synthesis of thioesters without the assistance of any directing group. A thio- ester moiety is created via successive CS and CO bond formation at the expense of three sp 3 CH bonds of the alkylbenzene and one sp 3 SH bond of the thiol.

A copper-catalyzed cross-dehydrogenative coupling strategy has been developed for the synthesis of two classes of esters from simple solvents. The reaction of methylarenes with cyclic ethers resulted in α-acyloxy ethers involving four sp(3) C-H cleavages, while treatment of methylarenes with cycloalkanes led to the formation of allyl esters at the expense of six consecutive sp(3) C-H bonds.

A variety of styrenes and phenylacetylenes serve as excellent arylcarboxy sources in bringing about substrate directed o-benzoxylation of 2-phenylpyridine derivatives catalyzed by Cu(II) in the presence of TBHP. This reaction proceeds via formation of phenylglyoxal followed by decarbonylation to benzoyl radical/benzaldehyde which acts as the arylcarboxy source.

A Cu(I)-catalysed synthesis of substituted 3-methyleneisoindolin-1-ones using alkynyl acids as an alkyne source has been developed. The reaction involves the decarboxylative cross-coupling of 2-halobenzamides with aryl alkynyl acids, followed by 5-exo-dig heteroannulation. While reactions of 2-iodo benzamides proceeded without a ligand, for 2-bromo substrates, the assistance of a ligand is essential.

Different reactivities and selectivities of Cu and Pd catalysts have been demonstrated in the reactions of benzylamines with 2-phenylpyridines. Although Pd is reported to give o-arylation (ArCO–), Cu introduces an arylcarboxy group (ArCOO–) at the proximal site of the directing group. For the first time benzylamine has been utilised as a synthetic equivalent of an arylcarboxy group.

An efficient metal free oxidative esterification of sp(3) C-H bonds (adjacent to an oxygen atom) in simple solvents like 1,4-dioxane, tetrahydropyran, tetrahydrofuran and ethyl acetate has been achieved using terminal aryl alkenes and alkynes as the ArCOO(-) sources.

Copper(I) catalysts are usually ineffective on the other hand Pd(II) catalysts are quite effective in promoting intramolecular sp 2 C–H functionalization (C–S bond formation). Herein, we have developed a ligand assisted Pd(II) catalyzed C–S bond formation via C–H activation from arylthioureas leading to the formation of 2-aminobenzothiazoles for substrates bearing electron donating (EDG) groups in the aryl ring. However without the assistance of ligand this Pd(II) catalyzed reaction is quite unproductive particularly for thioureas possessing strongly electron donating groups in the aryl rings. Interestingly, the ligand free Cu(II) catalyzed oxidative cyclization of arylthioureas are equally effective both for arylthioureas possessing electron donating as well as electron withdrawing groups in the aryl rings.

An efficient protocol has been developed for the direct ortho-hydroxylation of 2-arylbenzothiazole using Pd(OAc)2 as the catalyst and either of DIB/AcOH or Oxone®/TFA combinations under air atmosphere. Under both these conditions, the methodology tolerates a diverse array of substituents giving good to excellent yields of corresponding ortho-hydroxylated products. Regioselective hydroxylation is observed at the less sterically hindered site of the phenyl ring possessing substituents at its meta position.

A tandem and convergent approach to var- ious N-, O-, or S-containing azoles has been devel- oped by exploiting the thiophilic property of cop- per(I) iodide used in a catalytic quantity. The present protocol gives access to amino-substituted tetrazoles, triazoles, oxadiazoles and thiadiazoles via oxidative desulfurization of their respective precursors fol- lowed by inter- or intramolecular attack of suitable nucleophiles. For aminotetrazoles and triazoles an excellent regioselectivity has been achieved through proper tuning of the pKa values of the parent amines attached to unsymmetrical thioureas. The method represents an autocatalytic process in which cop- per(I) iodide gets converted to copper(II) sulfide which in turn transforms to active copper(II) oxide that effectively carries forward the catalytic cycle. The fate of the copper catalyst has also been studied using scanning electron microscopic (SEM) and energy-dispersive X-ray spectroscopic (EDS) analy- ses which give an insight into the mechanism for this catalytic process.

Copper(II) as the catalyst in a cross dehydrogenative coupling (CDC) reaction has been demonstrated for the synthesis of benzylic esters using aldehydes and alkylbenzenes as coupling partners.

A tandem regioselective one-pot synthesis of 3-amino-[1,2,4]-triazoles has been achieved from 1,3-disubstituted thioureas using molecular iodine. In this one-pot strategy, the intermediate carbodiimide generated in situ from thiourea upon reaction with HCONHNH2 gives diaryl/alkylhydrazinecarboximidamide or acylureidrazone, which then undergoes an intramolecular cyclodehydration to afford the corresponding 3-amino-[1,2,4]-triazole. The product regioselectivity for unsymmetrical 1,3-disubstituted thioureas correlate well with the pKas of the parent amines attached, in which the amine having higher pKa goes to the ring nitrogen while the other nitrogen remains flanked as an exocyclic nitrogen of the triazole core. This method is milder and environmentally sustainable giving good to excellent yields of the desired products.

A direct access to symmetrical and unsymmetrical 2,5-disubstituted [1,3,4]-oxadiazoles has been accomplished through an imine C-H functionalization of N-arylidenearoylhydrazide using a catalytic quantity of Cu(OTf)(2). This is the first example of amidic oxygen functioning as a nucleophile in a Cu-catalyzed oxidative coupling of an imine C-H bond. These reactions can be performed in air atmosphere and moisture making it exceptionally practical for application in organic synthesis.

An efficient process for the oxidative coupling of a variety of phenols having an ortho-benzothiazole substituent, 8-hydroxyquinoline and ortho-formyl phenols with N,N-dialkylformamides using tBuOOH as the oxidant in the presence of a Cu(II)-catalyst is presented.

A unique copper-catalyzed cross-dehydro- genative coupling (CDC) of thiols and alkylbenzenes has been developed for the synthesis of thioesters without the assistance of any directing group. A thio- ester moiety is created via successive CS and CO bond formation at the expense of three sp 3 CH bonds of the alkylbenzene and one sp 3 SH bond of the thiol.

A copper-catalyzed cross-dehydrogenative coupling strategy has been developed for the synthesis of two classes of esters from simple solvents. The reaction of methylarenes with cyclic ethers resulted in α-acyloxy ethers involving four sp3 C–H cleavages, while treatment of methylarenes with cycloalkanes led to the formation of allyl esters at the expense of six consecutive sp3 C–H bonds.

Chloride and fluoride can act as leaving group as well, yet requiring longer reaction time and giving lower yields.

Copper(I) catalysts are usually ineffective on the other hand Pd(II) catalysts are quite effective in promoting intramolecular sp 2 C–H functionalization (C–S bond formation). Herein, we have developed a ligand assisted Pd(II) catalyzed C–S bond formation via C–H activation from arylthioureas leading to the formation of 2-aminobenzothiazoles for substrates bearing electron donating (EDG) groups in the aryl ring. However without the assistance of ligand this Pd(II) catalyzed reaction is quite unproductive particularly for thioureas possessing strongly electron donating groups in the aryl rings. Interestingly, the ligand free Cu(II) catalyzed oxidative cyclization of arylthioureas are equally effective both for arylthioureas possessing electron donating as well as electron withdrawing groups in the aryl rings.

The ortho carbonyl group in hydroxyarenes (I) is essential for the oxidative aroylation of the OH-group with alkylbenzenes in the presence of tBu-OOH as oxidant.

By using alkylbenzenes as aroyl surrogates, copper(II) catalyzed chemoselective O-aroylations of 1,3-dicarbonyl compounds and phenolic −OH ortho to carbonyl (−CHO, −COR) groups have been achieved. A dual mechanism operating in tandem for these transformations has been supported by a crossover experiment.

An efficient protocol has been developed for the direct ortho-hydroxylation of 2-arylbenzothiazole using Pd(OAc)2 as the catalyst and either of DIB/AcOH or Oxone®/TFA combinations under air atmosphere. Under both these conditions, the methodology tolerates a diverse array of substituents giving good to excellent yields of corresponding ortho-hydroxylated products. Regioselective hydroxylation is observed at the less sterically hindered site of the phenyl ring possessing substituents at its meta position.

A tandem regioselective one-pot synthesis of 3-amino-[1,2,4]-triazoles has been achieved from 1,3-disubstituted thioureas using molecular iodine. In this one-pot strategy, the intermediate carbodiimide generated in situ from thiourea upon reaction with HCONHNH2 gives diaryl/alkylhydrazinecarboximidamide or acylureidrazone, which then undergoes an intramolecular cyclodehydration to afford the corresponding 3-amino-[1,2,4]-triazole. The product regioselectivity for unsymmetrical 1,3-disubstituted thioureas correlate well with the pKas of the parent amines attached, in which the amine having higher pKa goes to the ring nitrogen while the other nitrogen remains flanked as an exocyclic nitrogen of the triazole core. This method is milder and environmentally sustainable giving good to excellent yields of the desired products.

Copper(II) as the catalyst in a cross dehydrogenative coupling (CDC) reaction has been demonstrated for the synthesis of benzylic esters using aldehydes and alkylbenzenes as coupling partners.

Thiosemicarbazides (I) and (III), generated in situ from dithiocarbamate salts and formic hydrazide and benzhydrazide, are converted into oxadiazoles (II) and (IV) by cyclodesulfurization with molecular iodine.

A direct access to symmetrical and unsymmetrical 2,5-disubstituted [1,3,4]-oxadiazoles has been accomplished through an imine C–H functionalization of N-arylidenearoylhydrazide using a catalytic quantity of Cu(OTf)2. This is the first example of amidic oxygen functioning as a nucleophile in a Cu-catalyzed oxidative coupling of an imine C–H bond. These reactions can be performed in air atmosphere and moisture making it exceptionally practical for application in organic synthesis.

A one-pot, tandem process has been developed for the synthesis of a library of tetrazoles from aryl isothiocyanates. Condensation of aryl isothiocyanates with ammonia, and aryl amines (R-NH2) provided mono, 1,3-disubstituted symmetrical and unsymmetrical thioureas, which on desulfurization with molecular iodine (I2) led to formation of the corresponding heterocumulene (cyanamides or carbodiimides). The in situ generated heterocumulene on subsequent treatment with sodium azide at room temperature gave corresponding tetrazoles. The product regioselectivity for unsymmetrical 1,3-disubstituted thioureas was found to be correlated with the basicities (pKa's) of the parent amines attached to the thiourea. Aryl-sec-alkyl unsymmetrical thioureas gave thioamido guanidino products rather than the 5-aminotetrazoles produced by HgCl2 mediation of the reaction. Bis-thioureas derived from aryl isothiocyanates and hydrazine gave thiadiazoles exclusively.

An “on-water” one-pot process has been engineered for the preparation of 2-aminobenzothiazole from ortho-halo (–F, –Cl, –Br and –I) substituted unsymmetrical thioureas. For ortho –I and –Br substrates the reactions afford 2-aminobenzothiazoles under metal free condition promoted by base. However, the relatively inert ortho –Cl and –F substrates undergo intramolecular arylthiolation only in the presence of CuO nanoparticles yielding 2-aminobenzothiazoles. This methodology provides easy access to aminobenzothiazoles utilising even the ortho –Cl and –F substrates. The catalyst is recyclable several times without loss of substantial activity. Other remarkable features include the wide range of functional group tolerance, absence of chromatographic purification (for ortho –I and –Br substrates) and providing moderate to excellent yield of the products under mild conditions, thus rendering the methodology as a highly eco-friendly alternative to the existing methods.

A one-pot, tandem process has been developed for the synthesis of a library of tetrazoles from aryl isothiocyanates. Condensation of aryl isothiocyanates with ammonia, and aryl amines (R-NH(2)) provided mono, 1,3-disubstituted symmetrical and unsymmetrical thioureas, which on desulfurization with molecular iodine (I(2)) led to formation of the corresponding heterocumulene (cyanamides or carbodiimides). The in situ generated heterocumulene on subsequent treatment with sodium azide at room temperature gave corresponding tetrazoles. The product regioselectivity for unsymmetrical 1,3-disubstituted thioureas was found to be correlated with the basicities (pK(a)'s) of the parent amines attached to the thiourea. Aryl-sec-alkyl unsymmetrical thioureas gave thioamido guanidino products rather than the 5-aminotetrazoles produced by HgCl(2) mediation of the reaction. Bis-thioureas derived from aryl isothiocyanates and hydrazine gave thiadiazoles exclusively.