1 aldehyde protection dithianes, hydrolysis with

Protection of 194 as a p-methoxybenzylether and subsequent epoxydation led to the trans-epoxide 195, which was transformed into the unsaturated aldehyde 196 by a three-reaction sequence, including regioselective oxirane opening with a 1,3-dithiane anion, hydrolysis of the dithioacetal formed, and dehydration. Chlorite promoted aldehyde oxidation, methyl ester formation, and removal of the hydroxyl protections delivered methyl (+)-shikimate 197 in a remarkable 12% yield from 193. 

The synthesis began with the treatment of 3,4-anhydro-l,2-0-isopropylidene-D-erythritol 90 with 2-alkyl-2-lithio-l,3-dithiane 92 to give 93 (Scheme 16). Reductive desulfurization of 93 and transacetalization of the resulting 94 by the following reaction sequence (1. acidic hydrolysis 2. protection of the primary hydroxyl group 3. ketalization and 4. basic hydrolysis) afforded the primary alcohol 95. The Swern oxidation of 95 yielded the aldehyde 96. 

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