ABSTRACT
Halomethyleneiminium bromides have also been used to convert alcohols in sugars, and nucleosides into the corresponding bromides. A simple procedure for converting alcohols into chlorides employs chloromethyleneiminium chloride. The reaction has been shown to proceed with inversion of configuration; the formation of 2-chlorooctane from 2-octanol proceeds with 100% inversion. Chloromethyleneiminium chlorides convert straight chain, branched, and polyfunctionalized alcohols into the corresponding chlorides. Reaction of conjugated enones that are part of the steroidal ring system can lead to vinyl chlorides. Chloroacrylaldehydes which are not substituted at the a-position undergo fragmentation induced by alkali to give a valuable synthetic route to terminal alkynes. The methyl group of some 4-methylpyrylium salts can also be similarly attacked by Vilsmeier reagents, which afford an enamine group at the 4-position. The procedure is satisfactory for short chain aliphatic a-formyl esters. The location of an exocyclic methylene group on a steroidal framework determines the extent of reaction with Vilsmeier reagents.
