Ultrasound‐mediated synthesis of camphoric acid‐based chiral salens for the enantioselective trimethylsilylcyanation of aldehydes

Abstract

New chiral salen ligands were prepared by the ultrasound-irradiated condensation of optically active (1R, 3S)-1,2,2-trimethyl-1,3-diaminocyclopentane with aromatic 1-hydroxyaldehydes. The ultrasound-mediated process is more convenient due to shorter reaction times, energy economy, and easier isolation of the products. The in situ formed Ti(IV)(salen) complexes, evaluated as catalysts in the enantioselective trimethylsilylcyanation of benzaldehyde, were found to be efficient for this process, originating the corresponding product in high yields (72-99%) and selectivities of up to 79%. The lowest energy transition states were determined by computational studies. These results were in qualitative agreement with the experimentally observed ones.

Synthesis, Characterization and Evaluation of the Antibacterial and Antitumor Activity of HalogenatedSalen Copper (II) Complexes derived from Camphoric Acid

“…( 1R,3S )‐1,3‐diamino‐1,2,2‐trimethylcyclopentane ( 1 ) was obtained from ( 1R,3S )‐camphoric acid in a simple one‐step procedure . Subsequent condensation of ( 1 ) with 2,5‐dibromosalicylaldehyde, 5‐chlorosalicylaldehyde or 2,5‐dichlorosalicylaldehyde in ethanol, in the presence of activated silica gel, under ultrasound irradiation for 30 minutes at room temperature, gave the halogenated salen ligands 2a‐2c , Scheme .…”

Synthesis, characterization and assessment of the cytotoxic activity of Cu(II), Fe(III) and Mn(III) complexes of camphoric acid‐derived salen ligands

“…The diamine 2 was obtained directly from (1 R ,3 S )‐camphoric acid ( 1 ) according to a slightly modified literature procedure (Scheme ). Subsequently, in order to obtain the salen ligand 3 , the diamine was condensed with two equivalents of salicylaldehyde in dichloromethane, in the presence of silica gel, under ultrasound irradiation for 30 min at room temperature as previously described by us …”

“…All solvents were purified or dried prior to use following standard procedures. Compound 3 was synthesized according to our previously described procedure . Infrared spectra were recorded with a Thermo Scientific Nicolet 6700 FTIR (solids were processed as KBr pellets).…”

“…Herein we describe the synthesis and characterization of Cu(II), Fe(III) and Mn(III) metal complexes ( 4a , 4b , 4c ) of (1 R ,3 S )‐ N , N ′‐bis[salicylidene]‐1,3‐diamino‐1,2,2‐trimethylcyclopentane ( 3 ), a salen previously synthesized by us for use in catalytic processes . The salen ligand 3 results from the condensation of (1 R ,3 S )‐1,3‐diamino‐1,2,2‐trimethylcyclopentane ( 2 ), a diamine derived from camphoric acid, with salicylaldehyde.…”

Enantioselective ethylation of aldehydes with 1,3-N-donor ligands derived from (+)-camphoric acid

“…16 (+)-Camphoric acid allows the preparation of a 1,3-diamine directly in one step, by the Schmidt reaction. This diamine can easily be converted into several derivatives, namely sulfonamide and amide type ligands, via one or two additional steps.…”