3,4,5-Trimethoxybenzaldehyde → trans-2,4-Bis-(3,4,5-trimethoxyphenyl)-1,3-dithiolane

Participants

Reaction Steps

1-(3,4,5-trimethoxyphenyl)-1,2-ethanedithiol (38) (0.56 g, 2.15 mmole), 3,4,5-trimethoxybenzaldehyde (24) (0.35 g, 1.78 mmole) and 0.178 g of pyridinium paratoluene sulfonate are added to 40 ml dry benzene and refluxed with Dean-Stark removal of the benzene-water azeotrope for 24 hours. The benzene is removed in vacuo, and the remaining oil redissolved in ethyl acetate. The organic layer is washed with H2O and was dried over MgSO4, filtered, and evaporated in vacuo to a white foam which is purified by flash column chromatography using 1:1 hexane/ethyl acetate as eluent (0.630 g, 81%). The trans isomer is isolated from the 1:1 mixture of diastereomers after three recrystallizations from methanol (25 mg). If the above reaction is performed under reduced pressure (aspirator) at 45° C. for 2.5 hours using camphor sulfonic acid as the catalyst, the product mixture contains a 3:1 cis/trans ratio of diastereomers. The cis diastereomer is isolated from this product mixture by recrystallization from either methanol or hexane/ethyl acetate.

Provenance & Evidence