Combinatorial Synthesis of Oxazol-Thiazole Bis-Heterocyclic Compounds

A combinatorial library of novel oxazol-thiazole bis-heterocycles was synthesized in good to excellent overall yields with high purity using a solution and solid-phase parallel synthesis approach. Oxazole amino acids, prepared from serine methyl ester and amino acids via coupling and cyclodehydration, were treated with Fmoc-NCS and α-haloketones for the parallel synthesis of diverse bis-heterocycles. Fmoc-isothiocyanate is used as a traceless reagent for thiazole formation. Oxazole diversity can be achieved by using variety of amino acids, whereas thiazole diversity is produced with various haloketones

Copper(I)-catalyzed cascade synthesis of 2-substituted 1,3-benzothiazoles: direct access to benzothiazolones

An efficient cascade process for the preparation of 2‐substituted 1,3‐benzothiazoles directly from 2‐haloaryl isothiocyanates and O or S nucleophiles by a Cu‐catalyzed, intramolecular, C–S bond formation has been developed. This cascade method is viable for the efficient syntheses of both O‐ and S‐substituted 1,3‐benzothiazoles. Furthermore, 1,3‐benzothiazol‐2(3H)‐ones having an alkyl group allow easy access to 1,3‐benzothiazolones

Self-assembled superstructure of xanthene derivatives

Various multi carbon homologations of 9-phenyl-9H-xanthen-9-ol (1) were obtained through a C-C bond formation by reacting it with various enolisable ketones in the presence of 1,1′-(ethane-1,2-diyl)dipyridinium bistribromide (EDPBT). All the ten derivatives along with the starting xanthen-9-ol have been characterized by single crystal X-ray diffraction. They all form self-assembled superstructure in the solid state. The self-assembling patterns in these supramolecular architectures were explained based on steric and electronic nature of the pendant arm

Arylthioureas with bromine or its equivalents gives no ‘Hugerschoff’ reaction product

The in situ generated aryl–alkyl unsymmetrical thiourea obtained by the reaction of an aryl isothiocyanate with an aliphatic secondary amine on treatment with bromine or its equivalent gave exclusively a product having a thioamido guanidino moiety and not the expected Hugerschoff product 2-aminobenzothiazole. A plausible reaction mechanism has been proposed for this unprecedented transformation and the scope has been extended to various substrates

Syntheses and regiochemistry of enol addition to 9-phenyl-9H-xanthen-9-ol

Regioselective C–C bond formation of 9-phenyl-9H-xanthen-9-ol 1 with various enolizable ketones I–X in an acidic (HBr) medium, obtained by the reaction of 1,1′-(ethane-1,2-diyl)dipyridinium bistribromide (EDPBT) with ketone is observed. Except for ketone, 4-methyl-pentan-2-one VII in all other cases examined the attack to xanthenyl carbocation is from the thermodynamically stable enolizable side of the unsymmetrical ketones. In the case of 3-methyl-butan-2-one VIII the equilibrium is in favor of the more stable enolizable ketone, which has large steric factor, hence no reaction was observed during its addition to alcohol 1

A convenient one-pot synthesis of thiazol-2-imines: application in the construction of pifithrin analogues

For the first time a reaction intermediate has been isolated giving further insight into the mechanism of thiazol-2-imine formation. The first step of the reaction requires a basic medium, while the second step is an acid mediated E1 elimination reaction. An efficient one-pot synthesis of substituted thiazol-2-imines have been achieved by the condensation of carbonyl compounds with thioureas and 1,3-disubstituted thioureas using 1,1′-(ethane-1,2-diyl)dipyridinium bistribromide (EDPBT). Unsymmetrical 1,3-disubstituted thioureas give regioselective products with symmetrical ketones, which are mainly governed by the p K a s of NH protons of thiourea, whereas symmetrical 1,3-disubstituted thioureas give regioselective products with symmetrical carbonyl compounds owing to the regioselective bromination of ketones. The methodology is extended to access novel neurodegenerative drug candidate pifithrin-α analogues in good yields in shorter reaction time. This method is simple, versatile and is applicable for different 1,3-disubstituted thioureas as well as a range of carbonyl compounds

Intra- and intermolecular C−S bond formation using a single catalytic system: first direct access to arylthiobenzothiazoles

We have for the first time developed two ligand-assisted Cu(I)-catalyzed sequential intra- and intermolecular S-arylations leading to the direct synthesis of arylthiobenzothiazoles in one pot without an inert atmosphere. Low catalyst loading, inexpensive metal catalyst and ligand, lower reaction temperature, and shorter reaction times make this method superior to all reported methods for the synthesis of arylthiobenzothiazole

Copper(I)-catalyzed synthesis of substituted 2-mercapto benzimidazole

An efficient method for the preparation of various substituted 2-mercapto benzimidazoles from their corresponding thioureas has been developed. S-Alkylation of thioureas followed by Cu-catalyzed intramolecular N-arylation furnished substituted 2-mercapto benzimidazoles in high yields and short reaction times. Furthermore, 2-mercapto benzimidazoles substituted with a p-methoxybenzyl group allowed access to benzimidazole thiones

A new facile synthetic method for the construction of 1,3-oxathiolan-2-ylidenes

A new, convenient and efficient synthetic method for the construction of 1,3-oxathiolan-2-ylidenes via sodium borohydride reduction of the addition product of dithiocarbamic acid esters with α-bromoketones under basic conditions is reported. This method is general and applicable to a range of systems

A one-pot synthesis of 1,4-dithiins and 1,4-benzodithiins from ketones using the recyclable reagent 1,1′-(ethane-1,2-diyl)dipyridinium bistribromide (EDPBT)

A novel access to 1,4-dithiins and 1,4-benzodithiins from the corresponding ketones in one-pot using the recyclable reagent, 1,1′-(ethane-1,2-diyl)dipyridinium bistribromide (EDPBT) is described. This method is mild, simple, environmentally benign and is applied successfully for the ring expansion of 1,3-dithiolane to 1,4-dithiins and the ring expansion associated with aromatisation of cyclic ketones with or without double bonds in the ring. The main feature of this method is that EDPBT acts as a promoter in the formation of 1,3-dithiolane and as a reagent in the ring expansion step. The spent reagent can be recovered, regenerated and reused