Synthesis of substituted isoquinolines by electrophilic cyclization of iminoalkynes

The tert-butylimines of o-(1-alkynyl)benzaldehydes and analogous pyridinecarbaldehydes have been cyclized under very mild reaction conditions in the presence Of I-2, ICI, PhSeCl, PhSCl, and P-O-2-NC6H4SCl to give the corresponding halogen-, selenium-, and sulfur-containing disubstituted isoquinolines and naphthyridines, respectively. This methodology accommodates a variety of iminoalkynes and affords the anticipated heterocycles in moderate to excellent yields. Monosubstituted isoquinolines and naphthyridines have been synthesized by the metal-catalyzed ring closure of these same iminoalkynes. The silver-catalyzed ring closure is highly effective in cyclizing aryl-, alkenyl-, and alkyl-substituted iminoalkynes at 50 degreesC.