Ir(tri-N-heterocyclic carbene)-catalyzed upgrading of glycerol: C-C bond formation for the synthesis of α-hydroxy acids.

Ir(triNHC) complexes catalyzed glycerol and alcohol dehydrogenative coupling, yielding diverse α-hydroxy acids. Unlike conventional conditions, Ir(triNHC) facilitated additional C-C bond formation after lactic acid production from glycerol, exhibiting high TOFs. This protocol successfully converted 1,2-propanediol and sorbitol into α-hydroxy acids, highlighting biomass-derived sources' potential as valuable platform chemicals.

Synthesis of α-Hydroxy Acids via Dehydrogenative Cross-Coupling of a Sustainable C2 Chemical (Ethylene Glycol) with Alcohols.

Ir(NHC) (NHC, N-heterocyclic carbene)-catalyzed dehydrogenative coupling of sustainable ethylene glycol and various bioalcohols can produce industrially valuable α-hydroxy acids (AHAs). This study is the first to report the sustainable synthesis of higher Cn AHAs, in addition to glycolic acid (C2 AHA) and lactic acid (C3 AHA). This catalytic system can be recycled to the seventh cycle while maintaining good yields. A reaction mechanism, including facile dehydrogenation of each alcohol and fast cross-coupling of dehydrogenated aldehydes forming products, was proposed based on 18O- and 2H-labeling experiments and electron spray ionization-mass spectrometry (ESI-MS) and NMR spectral analyses.