Organocatalyzed Asymmetric Vinylogous Addition of Oxazole-2(3H)-thiones to α,β-Unsaturated Ketones: An Additive-Free Approach for Diversification of Heterocyclic Scaffold

Recent Advances in Greener Asymmetric Organocatalysis Using Bio-Based Solvents

Efficient synthetic methods that avoid the extensive use of hazardous reagents and solvents, as well as harsh reaction conditions, have become paramount in the field of organic synthesis. Organocatalysis is notably one of the best tools in building chemical bonds between carbons and carbon-heteroatoms; however, most examples still employ toxic volatile organic solvents. Although a portfolio of greener solvents is now commercially available, only ethyl alcohol, ethyl acetate, 2-methyltetrahydrofuran, supercritical carbon dioxide, ethyl lactate, and diethyl carbonate have been explored with chiral organocatalysts. In this review, the application of these bio-based solvents in asymmetric organocatalytic methods reported in the last decade is discussed, highlighting the proposed mechanism pathway for the transformations.

Diastereodivergent aminocatalyzed spirocyclization strategies using 4-alkylideneisoxazol-5-ones and methyl vinyl ketones

Diasterodivergent aminocatalyzed approaches starting from 4-alkylideneisoxazol-5-ones and methyl vinyl ketones have been developed for the synthesis of racemic 6,10-cis-spiroisoxazol-5-ones and highly enantioenriched 6,10-trans-spiroisoxazol-5-ones.

Enantiomeric ratios: Why so many notations?

The correct quantification of enantiomers is pivotal in a variety of fields, such as pharmacokinetic studies, enantioselective syntheses, chemical characterization of natural products, authentication of fragrance and food, biodegradation behavior, accurate evaluation of environmental risk, and it can also provide information for sentencing guidance in forensic field. Enantioselective chromatography is the first choice to assess the composition of an enantiomeric mixture. Different notations have been used to express the measured enantiomeric ratios, which compromise the results and represent a challenge for data comparison. This manuscript critically discusses the currently used notations and exemplifies with applications in different fields indicating the advantages and disadvantages of one of the adopted systems. In order to simplify the notations, the use of enantiomeric ratio (e.r.%) as standardization for nonchiroptical methods is proposed.