Ligand-Promoted [Pd]-Catalyzed α-Alkylation of Ketones through a Borrowing-Hydrogen Approach.

A new class of palladium complexes bearing bidentate 2-hydroxypyridine based ligands have been prepared and fully characterized. The applications of these new complexes towards ketone alkylation reactions with alcohols through a metal-ligand cooperative borrowing-hydrogen (BH) process were demonstrated.

A mononuclear iron(III) complex with unusual changes of color and magneto-structural properties with temperature: synthesis, structure, magnetization, multi-frequency ESR and DFT study.

From the reaction of 2-hydroxy-6-methylpyridine (L) with iron(II) tetrafluoroborate, a new mononuclear iron(III) octahedral complex [FeL6](BF4)3 has been isolated. The color of the complex reversibly changed from red at room temperature to yellow-orange at the liquid nitrogen temperature. Magnetization measurements indicate that iron(III) in [FeL6](BF4)3 is in a high-spin state S = 5/2, from room temperature to 1.8 K. The high-spin ground state of iron(III) is also confirmed by DFT calculations. Although the spin-crossover of the complex is not observed, X-band and multifrequency high-field/high-frequency electron spin resonance (ESR) spectroscopy shows rather uncommon iron(III) spectra at room temperature and an unusual change with cooling. Spectral simulations reveal that the S = 5/2 ground state multiplet of the complex can be characterized by the temperature independent axial zero-field splitting parameter of |D| = +2 GHz (0.067 cm-1) while the value of the rhombic parameter E of the order of some tenths MHz increases on lowering the temperature. Single crystal X-ray diffraction (SCXRD) shows that the iron(III) coordination geometry does not change with temperature while supramolecular interactions are temperature dependent, influencing the iron(III) rhombicity. Additionally, the DFT calculations show temperature variation of the HOMO-LUMO gap, in agreement with the changes of color and ESR-spectra of the iron(III) complex with temperature.

Synthesis of Highly Substituted Biaryls by the Construction of a Benzene Ring via In Situ Formed Acetals.

Herein, we present an interesting method for the construction of a benzene ring using propargylic alcohols and 1,3-dicarbonyls, which involves three new C-C bond formations via cascade alkylation, formylation, annulation, and aromatization to make substituted biaryls. This one-pot Brønsted acid-promoted protocol utilizes the unique reactivity of the acetal formed under the reaction conditions. Alkynyl methyl ketones could be employed instead of 1,3-dicarbonyls as they are converted to 1,3-dicarbonyls by hydration under the reaction conditions.

Ru-Catalyzed Cross-Dehydrogenative Coupling between Primary Alcohols to Guerbet Alcohol Derivatives: with Relevance for Fragrance Synthesis.

A simple method has been developed for the cross dehydrogenative coupling between two different primary alcohols using readily available RuCl2(PPh3)3 as a precatalyst through the borrowing-hydrogen approach. The present methodology is applicable to a large variety of alcohol derivatives including long chain aliphatic alcohols and heteroaryl alcohols. In addition, the methodology was applied in a straightforward protocol to synthesize commercially available fragrances such as Rosaphen and Cyclamenaldehyde in good yields.

Ru-Catalyzed Completely Deoxygenative Coupling of 2-Arylethanols through Base-Induced Net Decarbonylation.

Substituted arylethanols can be coupled by using a readily available Ru catalyst in a fully deoxygenative manner to produce hydrocarbon chains in one step. Control experiments indicate that the first deoxygenation occurs through an aldol condensation, whereas the second occurs through a base-induced net decarbonylation. This double deoxygenation enables further development in the use of alcohols as versatile and green alkylating reagents, as well as in other fields, such as deoxygenation and upgrading of overfunctionalized biomass to produce hydrocarbons.

In Situ Formed Acetal-Facilitated Synthesis of Substituted Indene Derivatives from o-Alkenylbenzaldehydes.

A new protocol has been developed for the synthesis of indene derivatives in a diastereoselective manner from o-alkenylbenzaldehydes and enolizable ketones in the presence of trimethyl orthoformate and catalytic triflic acid. This method involves tandem in situ formed acetal-assisted Claisen-Schmidt condensation followed by 5-exo-trig cyclization/Michael addition in one-pot. It has also been shown that the chalcones derived from o-alkenylbenzaldehydes and ketones can effectively be transformed into indene derivatives in the presence of TfOH catalyst alone.

A facile access to substituted benzo[a]fluorenes from o-alkynylbenzaldehydes via in situ formed acetals.

In situ formed acetal changes the course of Brønsted acid-catalyzed reaction of ortho-alkynylbenzaldehydes with arylalkynes altogether. By utilizing this, an efficient domino approach for the regioselective synthesis of substituted benzo[a]fluorenes has been developed under mild reaction conditions. In situ formed acetal facilitates the intermolecular heteroalkyne metathesis and subsequent trans to cis isomerization of a double bond to effect the intramolecular annulation.

Synthesis of naphthalene derivatives from ortho-alkynylacetophenone derivatives via tandem in situ incorporation of acetal and intramolecular heteroalkyne metathesis/annulation.

An interesting domino reaction for the synthesis of substituted naphthyl ketones has been developed using readily accessible starting materials. This domino reaction proceeds via in situ incorporation of an acetal followed by intramolecular heteroalkyne metathesis/annulation in an ortho-alkynylacetophenone derivative. A deuterium incorporation experiment has been carried out to understand the mechanism.

Gold/copper-catalyzed activation of the aci-form of nitromethane in the synthesis of methylene-bridged bis-1,3-dicarbonyl compounds.

Activation of the aci-form of nitromethane using Lewis acids for the attack of carbon nucleophiles was studied. 1,3-Dicarbonyl compounds in the presence of catalytic amounts of AuCl(3) or Cu(OTf)(2) in nitromethane solvent could be converted into methylene-bridged bis-1,3-dicarbonyl compounds.