PIDA mediated oxidative annulation of aryl methyl ketones: a facile approach for the chemoselective synthesis of 5-substituted oxazoles

We have developed a simple and efficient protocol for the chemoselective synthesis of 5-substituted oxazoles via oxidative annulation of substituted acetophenones with NH4OAc and DMSO using PIDA as an effective oxidant. NH4OAc and DMSO act as less toxic one nitrogen and one carbon synthons, respectively. It is a metal-free, step and atom economical approach with good functional group tolerance and chemoselectivity.

Tricyclic 2-benzazepines obtained via an unexpected cyclization involving nitrilium ylides

Attempted use of (E)-3-arylidene-4-diazopyrrolidine-2,5-diones in the Rh(ii)-catalyzed condensation with nitriles to form 1,3-oxazoles led to an unexpected outcome. The nitrilium ylide species thought to form on Rh(ii)-catalyzed decomposition of diazo compounds underwent a cyclization onto the nearby arylidene moiety followed by 1,5-hydride shift. This led to the formation of a 2-benzazepine core which has special significance for drug discovery and can be considered a privileged scaffold.

Synthesis of Amido Sulfonamido Heteroaromatics Under Ultrasonication and Their Antimicrobial Activity

A convenient and facile methodology for N-sulfonylation of heteroaryl amines with ethyl chlorosulfonylacetate in the presence of dispersed sodium in THF under ultrasonication is reported. The corresponding heteroaryl sulfonamido esters are directly condensed with heteroaryl amines to get amido sulfonamido heteroaromatics in the presence of a mild base in THF under ultrasonication. Utilization of easy reaction conditions, shorter reaction times, and isolation of products in high yields under ultrasonication make this process as economically viable. The compounds 12c, 12d, 12f and 13f are potential antibacterial agents against B. subtilis and the compounds 12f, 13c and 13f are potential antifungal agents against A. niger.

Gold-catalyzed dual annulation of azide-tethered alkynes with nitriles: expeditious synthesis of oxazolo[4,5-c]quinolines

A gold-catalyzed dual annulation of azide-tethered internal alkynes, which provides convenient access to quinoline derivatives, has been reported.

Continuous multistep synthesis of 2-(azidomethyl)oxazoles

An efficient three-step protocol was developed to produce 2-(azidomethyl)oxazoles from vinyl azides in a continuous-flow process. The general synthetic strategy involves a thermolysis of vinyl azides to generate azirines, which react with bromoacetyl bromide to provide 2-(bromomethyl)oxazoles. The latter compounds are versatile building blocks for nucleophilic displacement reactions as demonstrated by their subsequent treatment with NaN₃ in aqueous medium to give azido oxazoles in good selectivity. Process integration enabled the synthesis of this useful moiety in short overall residence times (7 to 9 min) and in good overall yields.

Total Synthesis of the Cyclic Dodecapeptides Wewakazole and Wewakazole B

The cyclic dodecapeptides wewakazole and wewakazole B have been synthesized by a divergent strategy via a common tris-proline containing oxazole octapeptide and two separate bis-oxazole containing tetrapeptide units, followed by peptide coupling and macrocyclization. The three oxazole amino acid fragments are readily accessible by rhodium(II)-catalyzed amide N-H insertion of diazocarbonyl compounds, or by the cycloaddition of rhodium carbenoids with nitriles.

Transition-metal-free synthesis of oxazoles: valuable structural fragments in drug discovery

This review article encapsulates the recent developments in the metal-free approaches used to construct oxazole moiety.

Ligand promoted Pd-catalyzed dehydrogenative alkenylation of hetereoarenes

An efficient Pd-catalyzed cross-dehydrogenative coupling of heteroarenes with styrenes and other olefinic substrates has been developed. This alkenylation paradigm encompasses a wide range of substrates and provides a straightforward approach toward C2-E-alkenylated azole motifs.

Synthesis of Indoxylic Acid Esters by Rhodium-catalyzed Carbene N–H Insertion and Thermal Cyclization

Reaction between diethyl diazomalonate and a range of N-alkylanilines in the presence of a catalytic amount of rhodium(ii) acetate dimer afforded carbene N–H insertion to produce anilinomalonates in modest-to-good yields. Upon heating to a high temperature for a short time, the anilinomalonates underwent thermal cyclization to indoxylic acid esters.

C-H alkenylation of azoles with enols and esters by nickel catalysis

Rather u(Ni)que: Two new C-H alkenylation reactions, that is C-H/C-O alkenylation and decarbonylative C-H alkenylation, of azoles are uniquely catalyzed by Ni/dcype. These azole alkenylation reactions are successfully applied to the convergent formal synthesis of siphonazole B.

Room temperature copper(II)-catalyzed oxidative cyclization of enamides to 2,5-disubstituted oxazoles via vinylic C-H functionalization

A copper(II)-catalyzed oxidative cyclization of enamides to oxazoles via vinylic C-H bond functionalization at room temperature is described. Various 2,5-disubstituted oxazoles bearing aryl, vinyl, alkyl, and heteroaryl substituents could be synthesized in moderate to high yields. This reaction protocol is complementary to our previously reported iodine-mediated cyclization of enamides to afford 2,4,5-trisubstituted oxazoles.

Thiazole and oxazole alkaloids: isolation and synthesis

Thiazoles, oxazole and their corresponding reduced derivatives, thiazolines and oxazolines, are found in marine sources exhibiting significant biological activities. The isolation, synthetic, and biological studies of these natural products, covering literature from January 2007 to June 2010, are summarized.

Rhodium carbene routes to oxazoles and thiazoles. Catalyst effects in the synthesis of oxazole and thiazole carboxylates, phosphonates, and sulfones

Dirhodium tetraacetate catalyzed reaction of alpha-diazo-beta-keto-carboxylates and -phosphonates with arenecarboxamides gives 2-aryloxazole-4-carboxylates and 4-phosphonates by carbene N-H insertion and cyclodehydration. In stark contrast, dirhodium tetrakis(heptafluorobutyramide) catalysis results in a dramatic change of regioselectivity to give oxazole-5-carboxylates and 5-phosphonates. Alpha-diazo-beta-ketosulfones behave similarly and give 5-sulfonyloxazoles upon dirhodium tetrakis(heptafluorobutyramide) catalyzed reaction with carboxamides. The analogous reactions of thiocarboxamides give the corresponding thiazole-5-carboxylates, -phosphonates, and -sulfones.

Development of an oxazole conjunctive reagent and application to the total synthesis of siphonazoles

The preparation of 4-carbethoxy-5-methyl-2-(phenylsulfonyl)methyloxazole and its use in the elaboration of more complex oxazoles are described. A total synthesis of the unique natural products siphonazoles A and B, illustrates an application of this building block. A discussion of the biological activity of the siphonazoles is also presented.