Ji-Tai Li

D,L‐Proline was found to efficiently catalyze the one‐pot condensation of aromatic aldehydes, malononitrile, and dimedone (1,3‐cyclohexanedione or 3‐methyl‐1‐phenyl‐2‐pyrazolin‐5‐one) 2‐Amino‐3‐cycano‐4‐aryl‐7,7‐dimethyl‐5,6,7,8‐tetrahydrobenzo[b]pyrans and 6‐amino‐5‐cyano‐4‐aryl‐1,4‐dihydropyrano[2,3‐c]pyrazoles were synthesized by a grinding method under solvent‐free conditions. The reaction proceeded cleanly at room temperature to afford the products in good yields.

Titanium tetrachloride in ethyl acetate can be reduced by Mg powder to the corresponding low‐valent titanium complexes, which can reduce some aromatic aldehydes and ketones to the corresponding pinacols in 38–85% yields within 15–60 min at rt with stirring.

Pinacol coupling of aromatic aldehydes and ketones by Mg powder in 0.1‐mol/L ammonium bromide aqueous solution can lead to the corresponding pinacols in 22–90% yields within 1–3 h at rt under ultrasound irradiation.

Pinacol coupling of aromatic aldehydes by aqueous vanadium(II) solution under ultrasound irradiation at room temperature can lead to the corresponding pinacols in 54–93% yields within 15–30 min.

Knoevenagel condensation of malononitrile with aromatic aldehydes catalyzed by KF–Al2O3 under ultrasound irradiation in anhydrous ethanol results in the formation of arylmethylenemalononitriles in 73–97% yields within 15–60 min.