Catalyst-Free Aldol Additions of 1,3-Dicarbonyl Compounds

A metal-free strategy for the cross-dehydrogenative coupling of 1,3-dicarbonyl compounds with 2-methoxyethanol

Here, we report a metal-free approach for the construction of methylene-bridged bis-1,3-dicarbonyl compounds via cross-dehydrogenative coupling of 1,3-dicarbonyl compounds with 2-methoxyethanol. In addition, we have extended this methodology to synthesize tetra-substituted pyridine derivatives using 1,3-dicarbonyl, 2-methoxyethanol and NH₄OAc in one step. The key advantages include accepting a wide range of substrates, utilizing O₂ as the sole oxidant, and synthesizing biologically active compounds such as 1,4-dihydropyridine and pyrazole.

Highly Efficient and Diastereoselective Construction of Trifluoromethyl-Containing Spiro[pyrrolidin-3,2'-oxindole] by a Catalyst-free Mutually Activated [3+2] Cycloaddition Reaction

A catalyst-free self-catalyzed [3+2] cycloaddition reaction of isatin-derived α-(trifluoromethyl)imines with vinylpyridines is reported. The reaction offers a straightforward and atom-economical procedure for the preparation of a series of 5'-trifluoromethyl-spiro[pyrrolidin-3,2'-oxindoles] in excellent yields and diastereoselectivities. The reaction mechanism has been investigated by control experiments, DFT calculation of pK_a values and the kinetic profiles, revealing that this reaction featured the mutual activation between isatin-derived α-(trifluoromethyl)imines and vinylpyridine to generate the reactive species.

The Role of Water in the Catalyst-Free Aldol Reaction of Water-Insoluble N-Methyl-2,4-thiazolidinedione with N-Methylisatin from QM/MM Monte Carlo Simulations

The role of water in the uncatalyzed aldol reaction of N-methyl-2,4-thiazolidinedione with N-methylisatin is investigated through Monte Carlo statistical mechanics simulations that utilize free energy perturbation theory and the mixed quantum mechanics and molecular mechanics (QM/MM) model with PDDG/PM3 for the QM method in "on-water" and DMSO environments. There are several conceivable orientations between thiazolidinedione and isatin in the process of C-C bond formation. However, the formation of the C-C bond takes place between the re face of isatin and the si face of (E)-enol of the thiazolidinedione to form the preferred anti-type product, which results from enhanced hydrogen-bonding interactions between water molecules and the oxygen atoms undergoing bond breakage and bond formation during the reaction. Novel insights into the effect of water on the aldol reaction are presented herein.

In situ generation of less accessible Boc-imines from aldehydes: construction of a quaternary carbon by the Mannich reaction or unprecedented aldol reaction

Mannich reactions of β-dicarbonyls with in situ generated less accessible Boc-imines from aldehydes were achieved.

The long underestimated carbonyl function of carbohydrates – an organocatalyzed shot into carbohydrate chemistry

Several novel and highly stereoselective C–C bond formation processes of unprotected carbohydrates are described.

Solvent-free and catalysts-free chemistry: a benign pathway to sustainability

In the past decade, alternative benign organic methodologies have become an imperative part of organic syntheses and chemical reactions. The various new and innovative sustainable organic reactions and methodologies using no solvents or catalysts and employing alternative energy inputs such as microwaves, sonication, conventional and room temperature heating conditions, mechanochemical mixing, and high-speed ball milling are discussed in detail. Environmentally benign and pharmaceutically important reactions such as multicomponent, condensation, and Michael addition reactions; ring opening of epoxides; and oxidation and other significant organic reactions are discussed. An overview of benign reactions through solvent- and catalyst-free (SF-CF) chemistry and a critical perspective on emerging synergies between SF-CF organic reactions are discussed.

Stereoselective amine-catalyzed carbohydrate chain elongation

Aldol additions of unprotected carbohydrates to 1.3-dicarbonyl compounds have been described. This transformation is based on a dual activation by tertiary amines and 2-hydroxypyridine.