Dimethyl Disulfide → 2-(3,4-Dichlorophenyl)-3,4-dihydro-6-(methylthio)-2h-pyrano[2,3-b]pyridine

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Reaction Conditions

Reaction Steps

A solution of 3.6 g of 6-bromo-2-(3,4-dichlorophenyl)-3,4-dihydro-2H-pyrano[2,3-b]pyridine in a mixture of 50 ml of toluene and 25 ml of anhydrous ether was cooled to -100° C. under nitrogen and 3.8 ml of 2.9M tert-butyllithium/pentane was added dropwise over about 5 minutes while keeping the temperature below -100° C. This gave a deep blue-green mixture containing the lithio intermediate (i.e., lithium replacing the bromine in the starting material). After 20 minutes, 1.8 ml of dimethyldisulfide was added. The mixture was then allowed to warm to 0° C. and it was partitioned between ether and water. The ether layer was washed with aqueous saturated sodium chloride solution, dried over potassium carbonate and concentrated to a yellow oil which solidified on cooling. Column chromatography on silica gel (20% ethyl acetate/hexane) gave pure product which was further recrystallized from hexane/ethyl acetate to give 2-(3,4-dichlorophenyl)-3,4-dihydro-6-(methylthio)-2H-pyrano[2,3-b]pyridine as colorless needles melting at about 109°-111° C.

Provenance & Evidence