Tartaric acids Tautomerism

An efficient and simple kinetic resolution of the racemic Betti base 387 was achieved via its reaction with acetone in the presence of L-(- -)-tartaric acid. When a suspension of racemic 387 in acetone was treated with L-(- -)-tartaric acid, the (A)-enantiomer formed a crystalline L-tartrate salt 389 this was filtered off, and the (iJ)-enantiomer could be isolated as a naphth[l,2-< ]oxazine derivative 388 from the filtrate (Equation 41). Both enantiomers were obtained in excellent yields and ee s. The enantioseparation is presumed to take place via a kinetically controlled N,0-deketalization of the (3)-naphth[l,2-< ]oxazine derivative <2005JOC8617>. An improved method for the enantioseparation of 387 was developed by the reaction of the ring-chain tautomeric l,3-diphenyl-3,4-dihydro-2//-naphth[2,l-< ][l,3]oxazine (41 X, Y = H) and L-(-f)-tartaric acid, yielding the crystalline 389 in 85% yield <2007SL488>. 

The simplest member of the series of aliphatic a-keto acids is pyruvic acid. It is conveniently prepared by the distillation of tartaric acid with a dehydrating agent such as postassium hydrogen sulphate (Expt 5.173). The reaction probably involves dehydration to the tautomeric oxaloacetic acid (13) intermediate, which then decarboxylates by virtue of its constitution as a / -keto acid. 

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