Metal-free one-pot domino reaction: chemoselective synthesis of polyarylated oxazoles

A sequential reaction of picolinamide with benzaldehydes promoted by Pd(TFA)2: rapid access to 4,5-disubstituted 2-(pyridin-2-yl)oxazoles in n-octane

We developed a synthetic method for obtaining 4,5-disubstituted 2-(pyridin-2-yl)oxazoles from picolinamide and aldehydes by employing Pd(TFA)2 as the catalyst in n-octane. This cascade reaction involves the condensation of picolinamide and two aldehyde molecules promoted by trifluoroacetic acid (TFA) generated in situ from Pd(TFA)2. This one-pot protocol provides rapid access to synthetically valuable triaryloxazoles from readily available starting materials under mild conditions. An 18O labeling study revealed that this tandem reaction proceeded via a different reaction mechanism compared to the Robinson-Gabriel oxazole synthesis.

Synthesis of 2,4,5-Trisubstituted Oxazoles from Copper-Mediated Benzylic sp3 C-H Aerobic Oxidative Annulation of Ketones and Amines via a Cascade Reaction

The functionalization of sp³ carbons is deemed challenging in synthetic organic chemistry yet has tremendous potential in producing potent organic compounds. A facile synthesis of 2,4,5-trisubstituted oxazoles through an oxidative, copper-catalyzed, and solvent-free annulation is described. Various arylated oxazoles were efficaciously synthesized at a mild temperature from readily available substrates under a molecular oxygen atmosphere. Preliminary mechanistic studies suggested that the reaction proceeds via an anionic-type mechanism and indicated the formation of a keto-imine intermediate. The reaction is notable for the abstraction of six hydrogen atoms, the functionalization of one sp² carbon and two sp³ carbons, and the formation of C-O and C-N bonds.

Synthesis of Tetrahydrofuro[2,3-d]oxazoles and Oxazoles by Hypervalent Iodine (III)-Promoted [2 + 2 + 1] Annulation

Reaction of a hypervalent iodine reagent with bistriflimide efficiently promotes three-component regioselective cyclization of tetrahydrofuro[2,3-d]oxazoles and oxazoles from homopropargyl alcohols bearing a phenyl group, with different substituents on the aryl alkyne compounds affecting the selectivity of the resulting product. Utilizing the hydroxyethyl oxazole derivatives obtained in this research could aid in the development of various peroxisome proliferator-activated receptor agonist derivatives.

An umpolung strategy for intermolecular [2 + 2 + 1] cycloaddition of aryl aldehydes and nitriles: a facile access to 2,4,5-trisubstituted oxazoles

We have described the first example of an umpolung strategy for intermolecular [2 + 2 + 1] cycloaddition between two aryl aldehydes and a nitrile under the influence of TMSOTf that proceeds through the formation of N–C, O–C and C–C bonds providing a simple synthetic protocol for obtaining 2,4,5-trisubstituted oxazoles.

An unprecedented intermolecular [2 + 2 + 1] cycloaddition strategy between two aryl aldehydes and a nitrile, wherein one of the aryl aldehydes serves as a carbanion (or equivalent) in the presence of TMSOTf for obtaining oxazole framework is presented.

Recent Developments in Oxazole Derivatives as Anticancer Agents: Review on Synthetic Strategies, Mechanism of Action and SAR studies

BACKGROUND

Cancer is the world's third deadliest disease. Despite the availability of numerous treatments, researchers are focusing on the development of new drugs lacking resistance and toxicity issues. Many newly synthesized drugs fail to reach clinical trials due to poor pharmacokinetic properties. Therefore, there is an imperative requisite to expand novel anticancer agents with in vivo efficacy.

OBJECTIVE

This review emphasizes synthetic methods, contemporary strategies used for the inclusion of oxazole moiety, mechanistic targets along with comprehensive structure-activity relationship studies to provide perspective into the rational design of highly efficient oxazole-based anticancer drugs.

METHODS

Literature related to oxazole derivatives engaged in cancer research is reviewed. This article gives a detailed account of synthetic strategies, targets of oxazole in cancer, including STAT3, Microtubules, G-quadruplex, DNA topoisomerases, DNA damage, Protein kinases, miscellaneous targets, in vitro studies, and some SAR studies.

RESULTS

Oxazole derivatives possess potent anticancer activity by inhibiting novel targets such as STAT3 and G-quadruplex. Oxazoles also inhibit tubulin protein to induce apoptosis in cancer cells. Some other targets such as DNA topoisomerase enzyme, protein kinases, and miscellaneous targets including Cdc25, mitochondrial enzymes, HDAC, LSD1, HPV E2 TAD, NQO1, Aromatase, BCl-6, Estrogen receptor, GRP-78, and Keap-Nrf2 pathway are inhibited by oxazole derivatives Many derivatives showed excellent potencies on various cancer cell lines with IC50 values in nanomolar concentrations.

CONCLUSION

Oxazole is a five-membered heterocycle, with oxygen and nitrogen at 1 and 3 positions respectively. It is often combined with other pharmacophores in the expansion of novel anticancer drugs. In summary, oxazole is a promising entity to develop new anticancer drugs.

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.