First Enantioselective Synthesis of (-)-(2S,6S)-(6-Ethyltetrahydropyran-2-yl)formic Acid

We describe in this letter the first enantioselective synthesis of (-)-(2S,6S)-(6-ethyltetrahydropyran-2-yl)formic acid (2) in five steps (30% overall yield, 87% ee), from the commercial chiral template (R)-2,3-isopropylideneglyceraldehyde (4). The two stereogenic centers in 2 were controlled by diastereoselective Barbier allylation of 4 in aqueous media and an efficient Prins cyclization reaction between 5 with propanal.