Facile, efficient synthesis of polysubstituted thiazoles via α-nitroepoxides and thioureas

Substrate-dependent regiodivergence in [3 + 2] annulation reactions of 2-(phenacylethylidene)cyclobutanones with thioureas

The [3 + 2] annulation reaction between a thiourea, an ambident dinucleophile, and a 2-(phenacylethylidene)cyclobutanone, containing a novel pull-pull alkene system, could in principle proceed with several chemo- and regioselectivity profiles. Here we describe a convenient synthesis of the functionalized cyclobutanone substrates and show that they react with thioureas in a manner that is rationalized mechanistically in terms of the steric and electronic effects at play. The [3 + 2] annulation proceeds in mild, additive-free conditions to provide access to previously unknown cyclobutane-fused imidazolidine-2-thione and thiazolidine-2-imine derivatives in good yields.

Synthesis of bisnitroepoxides and their applications in the synthesis of bis(thiazolidine-2-thiones), bis(dithiocarbamates), bis(xanthates) and bis(thiazoles)

Novel bis(nitroepoxides) were prepared based on terephthaldehyde and isophthaladehyde and their reactions with diversities of nucleophiles such as primary and secondary amine-based dithiocarbamic acids, xanthates, and ammonia-based dithiocarbmamates were investigated for the synthesis of bis(thiazolidine-2-thiones), bis(dithiocarbamates), bis(xanthates) and bis(thiazoles), respectively. It provides simple access to complex molecules in one step in high to excellent yields.

Catalyst free one pot three components synthesis of 2-iminothiazoles from nitroepoxides and thiourea

Nitroepoxides were introduced as efficient substrates for the one-pot three-component synthesis of 2-iminothiazoles under catalyst-free conditions. Reaction of amines, isothiocyanates, and nitroepoxides in THF at 10-15 °C afforded corresponding 2-iminothiazoles in high to excellent yields. The reaction proceeds via the in situ formation of thiourea from an amine and an isothiocyanate, followed by nitroepoxide ring opening with the sulfur of thiourea, cyclization reaction, and dehydration cascade. The structures of products were confirmed by IR, NMR, HRMS analyses and X-ray crystallography.

Highly Chemoselective Synthesis of Purino[3,2-c]oxazoles via the Asymmetric Dearomative [3+2] Cycloaddition of Purines with Donor-Acceptor Oxiranes

A Ni(II)/bisoxazoline-catalyzed asymmetric dearomative [3+2] cycloaddition of substituted purines with donor-acceptor oxiranes was developed. This reaction, which proceeds via highly chemoselective C-C bond cleavage of the oxiranes, accesses chiral purino[3,2-c]oxazole compounds (≤99% ee after enrichment via crystallization). The electronic effects of the purine ring determine the reactivity of the substrate. The general applicability of this method was illustrated by gram-scale synthesis, the diverse transformations of the product, and the promising biological activities of selected derivatives.

Multicomponent synthesis of fully substituted thiazoles using glycine-based dithiocarbamates, acetic anhydride and nitroalkenes

Reaction of glycine-based dithiocarbamates with nitroalkenes in the presence of acetic anhydride was utilized for the synthesis of fully substituted 2-(alkylsulfanyl)-4-(nitroalkyl)-5-acyloxy-1,3-thiazoles. The reaction proceeds via the in situ formation of thiazol-5(4H)-one from glycine-based dithiocarbamates, followed by the Michael addition of this intermediate to nitroalkenes, aromatization, and esterification reaction cascade. This new one-pot three-component reaction afforded a diverse library of fully substituted thiazoles in high to excellent yields under solvent-free conditions.

Chemo- and regioselective ring-opening of donor-acceptor oxiranes with N-heteroaromatics

The first ring-opening of D-A oxiranes with N-heteroaromatics in a chemoselective C-C bond cleavage manner was achieved. In the presence of 5 mol% of Y(OTf)3 as the catalyst, diverse N-heteroaromatics, including benzotriazoles, purines, substituted benzimidazole, imidazole and pyrazole, reacted well with various D-A oxiranes, providing acyclic nucleoside analogues containing a N-glycosidic bond in up to 97% yield and up to >95 : 5 regioselectivity. Through simple transformation, the Ganciclovir analogue could also be obtained.

Cyclization Reaction of Donor-Acceptor Oxiranes with N,N'-Disubstituted Thioureas: A Domino Process to trans-Dihydropyrimidines

An unprecedented cyclization reaction of donor-acceptor oxiranes with N,N'-disubstituted thioureas to construct trans-dihydropyrimidines is presented. Preliminary reaction mechanism studies demonstrated that the reaction underwent sequential cycloaddition/amine ester exchange/oxygen-sulfur exchange/desulfuration/Michael addition process. A wide range of trans-dihydropyrimidines were produced with high yields up to 94% by using this method.

Regioselective Opening of Nitroepoxides with Unsymmetrical Diamines

Nitroepoxides are easily transformed into benzodiazepines, tetrahydrobenzodiazepines, imidazopyridines, and N-alkyl tetrahydroquinoxalines by treatment with 2-aminobenzylamines, 2-aminopyridines, and N-alkyl 1,2-diaminobenzenes, respectively. Regioselectivity is controlled through attack of the most nucleophilic nitrogen of the unsymmetrical diamine to the β position of the epoxide. These reactions represent an efficient way to prepare privileged bioactive structures.

Synthesis of N,S-Heterocycles and Dithiocarbamates by the Reaction of Dithiocarbamic Acids and S-Alkyl Dithiocarbamates with Nitroepoxides

A facile and efficient procedure for the synthesis of substituted thiazole-2(3H)-thiones and thiazolidine-2-thiones by the reaction of primary amines, carbon disulfide, and nitroepoxides is described. By using secondary amines in this protocol, the corresponding dithiocarbamate-substituted phenyl-2-propanones were prepared in excellent yields. In addition, substituted thiazoles and 1-(alkylthio)-1-phenylpropan-2-ones were prepared in reactions of S-alkyl dithiocarbamates and nitroepoxides.

Synergism of fused bicyclic 2-aminothiazolyl compounds with polymyxin B against Klebsiella pneumoniae

A series of fused bicyclic 2-aminothiazolyl compounds were synthesized and evaluated for their synergistic effects with polymyxin B (PB) against Klebsiella pneumoniae (SIPI-KPN-1712). Some of the synthesized compounds exhibited synergistic activity. When 4 μg ml-1 compound B1 was combined with PB, it showed potent antibacterial activity, achieving 64-fold reduction of the MIC of PB. Furthermore, compound B1 showed prominent synergistic efficacy in both concentration gradient and time-kill curves in vitro. In addition, B1 combined with PB also exhibited synergistic and partial synergistic effect against E. coli (ATCC25922 and its clinical isolates), Acinetobacter baumannii (ATCC19606 and its clinical isolates), and Pseudomonas aeruginosa (Pae-1399).

Access to Fully Substituted Thiazoles and 2,3-Dihydrothiazoles via Copper-Catalyzed [4 + 1] Heterocyclization of α-(N-Hydroxy/aryl)imino-β-oxodithioesters with α-Diazocarbonyls

An efficient chemoselective practical route to fully substituted thiazoles and 2,3-dihydrothiazoles has been devised by [4 + 1] heterocyclization of α-(N-hydroxy/aryl)imino-β-oxodithioesters with in situ generated Cu-carbenoids of diazocarbonyls. The α-(N-hydroxy/aryl)imino-β-oxodithioesters are readily accessible by the reaction of β-oxodithioesters with nitrous acid/nitrosoarenes. The overall transformation involves sequential N-O/C-N bonds cleavage followed by cascade C-N/C-S bonds formation in one-pot. This new strategy allows full control over the introduction of various sensitive functional groups at different positions of the thiazole ring, broadening the arsenal of synthetic methods to obtain such scaffolds.

Efficient construction of C–N and C–S bonds in 2-iminothiazoles via cascade reaction of enaminones with potassium thiocyanate

Regioselective cascade reactions have been developed by using enaminones and potassium thiocyanate, offering a novel protocol for the synthesis of thiazoles from enaminones.