2‐Bromo‐2‐chloro‐3‐arylpropanenitriles as C‐3 synthons for the synthesis of functionalized 3‐aminothiophenes
2-Bromo-2-chloro-3-arylpropanenitriles can be prepared by Meerwein reaction from 2-chloroacrylonitrile and various aryldiazonium salts under copper(II) bromide catalysis. They proved to be stable compounds which form 2-chlorocinnnamonitriles upon treatment with bases. Reaction of the title compounds with substituted thioglycolates gave substituted 3-aminothiophenes which have not yet been accessible by other routes. Three-component reactions with the title compound, sodium sulfide and bromonitromethane, chloroacetonitrile, or ethyl 4-chloroacetoacetate gave 2-nitro- and 2-cyano-substituted 3-aminothiophenes, and thienopyridinediones in high yields and in one single step, respectively.