Methylthiofurane: Herstellung und Reaktionen

Preparation and Reactions of Methylthiofurans By lithiation of 3,4‐dimethoxyfuran, 2‐methylfuran and furan, followed by reaction with dimethyldisulfide, the methylthiofurans 2, 8 , and 10 have been prepared. Reaction of 8 with maleic anhydride has yielded 6‐methyl‐3‐(methylthio)phthalic anhydride ( 9 ), a yellow substance with a strong greenish fluorescence, obviously formed by elimination of H 2 O from an unstable cycloadduct. An analgous reaction of 2 resulted in an unexpected mixture from which the following yellow compounds were isolated: 3‐hydroxy‐4,5‐dimethoxy‐6‐(methylthio)phthalic anhydride ( 3 ), 4‐hydroxy‐5‐methoxy‐3,6‐bis(methylthio)phthalic anhydride ( 4 ), and bis( S ‐methyl) (2 Z ,4 E ,6 Z )‐2,3,6,7‐tetramethoxy‐4,5‐bis(methylthio)‐2,4,6‐octatrienethioate ( 5 ). Compound 5 is also formed on standing of 2 at RT. Mild acid hydrolysis of 2 results in ring‐opening accompanied by an intramolecular oxido‐reduction to yield S ‐methyl(3 Z )‐3‐methoxy‐4‐(methylthio)‐2‐oxo‐3‐butenethioate ( 6a ). The structures of compounds 5 and 6a have been determined by X‐ray analysis.