Grignard reagents with sulphurous acid derivatives

TABLE 8. Formation of sulphoxides, R2S=0, from the reaction of Grignard reagents with sulphurous acid derivatives, SOX2... 

A mixture of 2-t-butylfuran and 2,5-di-t-butylfuran is obtained by the action of t-butyl chloride on furan in the presence of mesitylene nolybdenum tricarbonyl." The intermediate in the nitration of furan-2-aldehyde in acetic anhydride has been identified as compound (26). Treatment of 5-bromo-2-furoic acid with sulphur tetrafluoride in hydrogen fluoride yields the dihydrofuran (27). Bromo-furans are converted into aryl-furans by crosscoupling with aryl Grignard reagents in the presence of nickel(II)-phosphine complexes. 2-Furoic acid is lithiated at position 5, 3-furoic acid at C-2. 2-Methylfuran yields the 5-methylthio-derivative by lithiation and subsequent treatment with dimethyl disulphide. The corresponding phenylthio-compound (28) has been converted into a series of 4-substituted 2-methyl-furans (29 R = alkyl, MeaSi, CO2H, or RCHOH) by the sequence bromi-nation, lithiation, treatment with the appropriate electrophile, and, finally, desulphurization with Raney nickel. 2-Lithiofuran reacts with copper(II)... 

Harder nucleophiles often react with thiirans to give a predominance of attack at carbon, with consequent cleavage of the weak carbon-sulphur bond. This strategy has been used to prepare 7-oxa-4-thia-alk-l-enes from alkoxides, thiiran, and allyl chlorides, yS-mercaptoethyl sulphides from thiiran and thiolate ions, thiazines by the CujO-catalysed cyclization of the adducts of a-lithio-isocyanides with thiirans, tautomeric mixtures of (18) and (19) or (20) from thiiran and hydrazones, 7V-methylpyrrolidines from bis(epithio)linoleic acid and methylamine, and 2,4-dimethylhex-5-ene-2-thiol by addition of the Grignard reagent derived from 3-chlorobut-l-ene with 2,2-dimethylthiiran. Methylthiiran has been found to open... 

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