Asymmetric Desymmetrization of Oxetanes for the Synthesis of Chiral Tetrahydrothiophenes and Tetrahydroselenophenes

Stereoselective synthesis of tri-substituted tetrahydrothiophenes and their in silico binding against mycobacterial protein tyrosine phosphatase B

A facile approach to tri-substituted tetrahydrothiophenes via thia-Michael/aldol has been developed. The cascade reaction was carried out in the presence of 5 mol% of DABCO in ethyl acetate to afford diversely functionalized tetrahydrothiophenes (THTs) with excellent diastereoselectivity. The present methodology has broad substrate tolerance. Gram-scale reaction proceeds with equal efficiency. Functional group transformations further highlight the synthetic potential of the THTs. An asymmetric version of the cascade reaction has also been investigated and a maximum of 72% ee was observed with cinchonidine derived squaramide. Moreover, in silico based molecular docking followed by deep learning based affinity prediction and molecular dynamics simulation analysis indicate the synthesized THT derivatives can act as potent competitive inhibitors of MptpB at low micromolar to nanomolar concentrations. In silico ADME analysis further suggests the plausibility of these compounds to act as future anti-mycobacterial therapeutic leads.

Green Chemistry Meets Asymmetric Organocatalysis: A Critical Overview on Catalysts Synthesis

Can green chemistry be the right reading key to let organocatalyst design take a step forward towards sustainable catalysis? What if the intriguing chemistry promoted by more engineered organocatalysts was carried on by using renewable and naturally occurring molecular scaffolds, or at least synthetic catalysts more respectful towards the principles of green chemistry? Within the frame of these questions, this Review will tackle the most commonly occurring organic chiral catalysts from the perspective of their synthesis rather than their employment in chemical methodologies or processes. A classification of the catalyst scaffolds based on their E factor will be provided, and the global E factor (EG factor) will be proposed as a new green chemistry metric to consider, also, the synthetic route to the catalyst within a given organocatalytic process.

Recent Advances in Enantioselective Desymmetrizations of Prochiral Oxetanes

Strain relief of oxetanes offers a plethora of opportunities for the synthesis of chiral alcohols and ethers. In this context, enantioselective desymmetrization has been identified as a powerful tool to construct molecular complexity and this has led to the development of elegant strategies on the basis of transition metal, Lewis acid, and Brønsted acid catalysis. This review highlights recent examples that harness the inherent reactivity of prochiral oxetanes and offers an outlook on the immense possibilities for synthetic application.

Mild C-C Bond Formation via Lewis Acid Catalyzed Oxetane Ring Opening with Soft Carbon Nucleophiles

Mild oxetane opening by soft carbon nucleophiles has been developed for efficient C-C bond formation. In the presence of LiNTf₂ or TBSNTf₂ as catalyst, silyl ketene acetals were found to be effective nucleophiles to generate a wide range of highly oxygenated molecules, which are key substructure in natural products like polyketides. Furthermore, intramolecular oxetane opening by a styrene-based carbon nucleophile via a Prins-type process was also achieved with Sc(OTf)₃ as catalyst, leading to efficient formation of the useful 2,3-dihydrobenzo[b]oxepine skeleton.

Unusual Skeletal Reorganization of Oxetanes for the Synthesis of 1,2-Dihydroquinolines

Skeletal reorganization is a type of fascinating transformations owing to their intriguing mechanisms and utility in complex molecule synthesis. However, only a limited amount of examples are known for most functional groups. Herein, we describe such an unusual process of oxetanes. In the presence of In(OTf)₃ as catalyst, oxetane-tethered anilines reacted unexpectedly to form 1,2-dihydroquinolines. This process not only provides expedient access to dihydroquinolines, but also represents a new reaction of oxetane. Mechanistically, it is believed that the reaction proceeds through initial nitrogen attack rather than arene attack followed by a series of bond cleavage and formation events. Control experiments provided important insights into the mechanism.