Sulfurous Chlorides and Derivatives

The formation of the chiral formamidine 1658 from octahydroisoquinoline 1656 and the isocyanide 1657 derived from valinol tert-butyl ester gives an intermediate with high chirality-inducing potential, which, through further reaction steps, allows an asymmetric synthesis of (+)-morphinane with high enantiomeric purity ( 98% ee in the decisive asymmetric reaction step) [1229]. The isocyanide 1657 is obtained in 85% yield by dehydration of the corresponding formamide with thionyl chloride. 

Di-2-pyridyl sulfite 1660 is presented as a useful reagent for the preparation of isocyanides under mild conditions [1230], Yields given in the table therein are good (70-82% for test alkyl, benzylic, and aryl isocyanides). The reagent (prepared from 2-hydroxypyridine 1659 and thionyl chloride) is rather unstable, but can be stored in a refrigerator for a week without decomposition , according to the authors. 

A patent application in this field Process for preparing 2-(2,6-dichloroanilino)-imidazole has been filed [1231], using sulfuryl chloride as the dehydration reagent for the formamide. 

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