A biomimetic TK one-pot reaction using hydroxypyruvate and aldehydes to generate α,α′-dihydroxy ketones in water has recently been described. To investigate this tertiary-amine mediated reaction mechanism two approaches were used. Firstly, 13C labelled lithium hydroxypyruvate was synthesised and used to establish where hydroxypyruvate is incorporated in the product. In separate experiments reaction intermediates were also successfully intercepted and structurally identified using ESI-MS with tandem mass spectrometry ESI-MS/MS. These studies indicated that two mechanisms appear to be operating, one involving the addition of the tertiary amine catalyst to hydroxypyruvate, the other an aldol-based mechanism. Since the first mechanism may enable facial stereodifferentiation in the addition of intermediates to the aldehyde, a preliminary study on the use of chiral catalysts was performed and the first asymmetric organocatalytic synthesis of α,α′-dihydroxy ketones in aqueous media achieved, in up to 50% ee, using a quinine ether catalyst.
