Pinacolic Coupling of Aromatic Carbonyl Compounds Using Zn Powder in Aqueous Basic Media without Organic Solvents

Abstract

Treatment of aromatic carbonyl compounds with Zn powder in 10% aq NaOH solution without using any organic solvents under the mild conditions afforded the corresponding 1,2-diols in good yields.

Organic Reactions in Aqueous Media with a Focus on Carbon−Carbon Bond Formations: A Decade Update

“…Schwartz reported a stereoselective pinacol coupling with a cyclopentadienetitanium complex . Pinacol-type couplings were also developed by using a Zn−Cu couple, Mg, Mn, Zn, In, Sm, Al/NaOH (or KOH), Al/F - , Ga, Cd, and other metals in aqueous media (eq 124). Under sonication, Kim and co-workers 482 found that aromatic aldehydes homocoupled to generate pinacol-type products.…”

Dehalogenation of Aromatic Halides Using Metallic Calcium in Ethanol

“…On the other hand, we have been investigating for some time the reduction of some functions in water as a hydrogen source. For examples, we have previously reported the reduction and reductive coupling of imines ( , ) or carbonyl compounds ( − ) and the dehalogenation of aromatic halides ( − ) using metals in an aqueous solution. Moreover, we also found that the reaction of 4-chlorobiphenyl 1 with Raney Ni−Al alloy, in a diluted aqueous alkaline solution at 90 °C was very effective for the dehalogenation process, yielding biphenyl 2 (in 10% aqueous NaOH solution) or cyclohexylbenzene 3 (in 0.5% aqueous KOH solution), respectively () (Figure ).…”

Reduction and Coupling Reactions of Carbonyl Compounds Using Samarium Metal in Aqueous Media

“…(b) According to ref b, cyclohexanecarbaldehyde is reduced by Al/KF in aqueous medium to give 10% of cyclohexylmethanol. However, cyclohexanone and 2-hexanone cannot be reduced by using Al with various fluoride salts.…”

“…The protocol using Sm (3 molar proportions) in 2 M HCl/THF (5:1) was applied to the pinacolic coupling reactions of other benzaldehydes and aromatic ketones (eq 1 and Table ). In most cases, high yields of pinacols were obtained as mixtures of dl and meso isomers under such reaction conditions. , The pinacolic coupling reaction of benzophenone was also successfully carried out by using Sm in aqueous media to give a 94% yield of benzopinacol (entry 17, Table ). Unimolecular reduction, giving alcoholic products, was either a minor pathway or did not occur.…”