Acetal exchange with benzaldehyde dimethyl

Benzylidenation of (/ )-butane-1,2,4-triol using either benzaldehyde (with azeotropic removal of water) or acetal exchange with benzaldehyde dimethyl acetal gave essentially the same result a mixture of three acetals in the ratio 90 5 5. 

When either L-tartaric acid esters la,b or D-tartaric esters 2a,b are treated with benzaldehyde under acidic catalysis with Deair-Stark removal of generated water, good to excellent yields of either (4i ,5i )-(330) or (45, 5 S)-2-phenyl-l,3-dioxolane-4,5-dicarboxylates (331) are obtained [115,116]. Acetal exchange, which involves reaction of the tartaric diesters with benzaldehyde dimethyl acetal in the presence of an acid catalyst, is also an excellent protection method [117]. 

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