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.

A vinylogous Michael reaction of 2-furanone dimers with α,β-unsaturated nitroolefins for constructing chiral γ,γ-disubstituted butenolides

An asymmetric vinylogous Michael reaction of 2-furanone dimers with α,β-unsaturated nitroolefins utilizing bifunctional thiourea as a catalyst has been developed, which provides an easy access to a wide range of chiral γ,γ-disubstituted butenolides.

Transition Metal-Free Intermolecular C(sp2)-H Direct Amination of Furanones via a Redox Pathway

A direct C(sp²)-H amination of 2-furanones under metal-free conditions was realized. This unprecedented intermolecular C-H to C-N conversion provides rapid access to 4-amino-furanone derivatives and novel aza-heterocycle fused furanone skeletons. A redox mechanism based on a double-Michael-addition intermediate INT2 is proposed and detected by spectrometry.

Enantioselective Michael addition of malonates to α,β-unsaturated ketones catalyzed by 1,2-diphenylethanediamine

A general and highly enantioselective Michael addition of malonates to cinnamones and chalcones has been developed. The commercially available 1,2-diphenylethanediamine could be directly utilized as the organocatalyst to furnish the desired adducts in satisfactory yield (61–99%) and moderate to excellent enantiopurity (65 to >99% ee). β-Ketoester was also a competent donor and was employed to construct densely functionalized cyclohexenones via a tandem Michael-aldol condensation process.

1,2-Diphenylethanediamine could be directly utilized to promote the Michael addition of malonates and β-ketoesters to various α,β-unsaturated ketones.

In situ formed acetals facilitated direct Michael addition of unactivated ketones

A facile Michael addition of unactivated ketones under Brønsted acid conditions for the synthesis of 1,5-diketones.

Synthesis of furo[3,4-c]quinolin-3(1H)-one derivatives through TMG catalyzed intramolecular aza-MBH reaction based on the furanones

The first TMG catalyzed intramolecular aza-MBH reaction based on furanone derivatives for the construction of furo[3,4-c]quinolin-3(1H)-ones scaffold.

Asymmetric Michael addition reactions of nitroalkanes to 2-furanones catalyzed by bifunctional thiourea catalysts

The first bifunctional thiourea catalyzed asymmetric Michael addition reactions of nitroalkanes to 2-furanones are described.