Phosgene → 4-Isocyano-5,6-dihydro-1-benzothiophen-7(4H)-one

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Reaction Steps

Alternatively, formula (Ia) isocyanate can be prepared by reacting the N-formyl-4,5,6,7-tetrahydro-7-oxobenzo-[b]thiophen-4-amine of formula (IIIa) with phosgene in the presence of a tertiary amine, e.g. triethylamine, in an inert solvent such methylene chloride and other chlorinated hydrocarbons at a temperature between about 0° and 50° C and preferably between 15° and 30° C to obtain 4,5,6,7-tetrahydro-7-oxobenzo[b]thien-4-yl isocyanide of formula (IV), which is then oxidized with dimethylsulfoxide (DMSO) in the presence of anhydrous p-toluenesulfonic acid (pTSA) at a temperature between about 25° and 75° C, and preferably 25° and 50° C. The above-described reaction sequence may be graphically illustrated as follows: ##SPC3##

Provenance & Evidence