Catalysis by cobalt Schiff's base complexes in highly selective conversion of arylglyoxals to α-aryl-α-hydroxyacetic esters

The Construction of Quaternary Stereocenters by the Henry Reaction: Circumventing the Usual Reactivity of Substituted Glyoxals

“…It is known that, in alcohol solvents, arylglyoxals and their hydrates are almost quantitatively converted into the corresponding hemiacetals. [11] Therefore, our hypothesis was that direct nitromethane addition to the ketone should be possible in these solvents if it was faster than the equilibration between the hemiacetal and dicarbonyl forms of the glyoxal (Scheme 1).…”

“…Furthermore, arylglyoxal hydrates have been used as electrophiles in several enantioselective reactions. Examples include the enantioselective synthesis of mandelic acid derivatives by a Cannizaro reaction, [11] carbonyl-ene reactions with water-tolerant Pd II and Pt II complexes, [12] and organocatalytic cross-aldol reactions with aldehydes. [13] In all cases, the reaction takes place at the more-reactive aldehyde carbonyl group if anhydrous or hydrated glyoxals were used.…”

Biomimetic catalytic transformation of toxic α-oxoaldehydes to high-value chiral α-hydroxythioesters using artificial glyoxalase I

“…1a). From the synthetic chemistry point of view, the glyoxalase I-catalysed detoxification process, that is, conversion of glyoxals with thiol into α-hydroxy thioesters, can be regarded as a variant of enantioselective intramolecular Cannizzaro reactions7891011.…”

“…1b). Of note, on contrast to enzymes, enantioselective introduction of a proton to transient enediol intermediate via synthetic route might be extremely challenging to control it in terms of enantioselectivity due to the small size of the proton37891011.…”

Bis(N-propylsalicylideneaminato)cobalt(II)

“…Bis(N-n-propylsalicylideneaminato)cobalt(II) catalyzes the highly selective transformation of phenylglyoxal to α-phenyl-α-hydroxyacetic ester (eq 1). 1 After a solution of phenylglyoxal (1) (1.0 mmol) and N-n-propylsalicylidene Co II complex (2a) (0.2 mmol) in a mixture of i-PrOH (40 mL) and 1,2-dichloroethane (20 mL) was heated at 60 • C for 8 h under oxygen atmosphere, the metal complex was separated, and the solvent was evaporated to afford a 97:3 mixture of i-propyl mandelate (3) and i-propylphenyl glyoxylate (4) in 93% yield. Ni-Propylsalicylidene Co II complex (2b) also catalyzes this transformation; however, a lower yield (31%) of i-propyl mandelate (3) was obtained.The hydroxocobalt(III) complex, Co III (OH), 5 which is generated from irreversible oxidation of the Co II complex in alcoholic solvents, is believed to be the reactive catalytic species.…”