Application of Sharpless asymmetric epoxidation on the preparation of the optically active flavours 3‐methylthiohexanal and 5(6)‐butyl‐1,4‐dioxan‐2‐one

Abstract

Optically active 2,3-epoxyhexanol obtained from Sharpless asymmetric epoxidation (AE) was regioselectively reduced to 1,3-hexandiol or 1,2-hexandiol. 1,3-Hexandiol was converted to 3-mesyloxyhexyl acetate. The following reaction with CH3SK gave 3-methylthiohexanol, which was oxidized through Swern oxidation to produce 3-methylthiohexanal. 5-and 6-Butyl-1,4-dioxan-2-one were formed concurrently by the reaction of 1,2-hexandiol with 2-bromoacetic chloride and the ratio of 5-butyl isomer to 6-butyl isomer was about 1:4. The enantiomeric excess values of both enantiomers of 3-methylthiohexanal and 5(6)-butyl-1,4-dioxan-2-one were about 90%, which were very close to those of 2,3-epoxyhexanol (about 94% ee). No obvious racemization occurred during the transformation from the Sharpless AE products to the final products.

Preparation and Odour Properties of (S)-3-Mercapto-1-Heptyl Acetate

“…25 (2R,3R)-2,3-Epoxy-1-heptanol (2R,3R)-4: The procedure used was similar to that used in our previous work. 26 Crushed 4Å molecular sieves were heated in a vacuum oven at 200 °C and 1 mmHg for at least 3 h. Dichloromethane was distilled over CaH 2 . An oven-dried 250 mL three-necked round-bottomed flask equipped with a magnetic stirbar, pressure equalising addition funnel, thermometer, nitrogen inlet, and bubbler was charged with 4Å powered activated molecular sieves (4.0 g) and dry CH 2 Cl 2 (200 mL).…”