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), ICl, PhSeCl, PhSCl, and p-O(2)NC(6)H(4)SCl 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 degrees C.

Substituted isoquinolines and naphthyridines have been prepared in good to excellent yields by the reaction of iminoalkynes with a variety of electrophiles under mild reaction conditions. Reaction: see text.

A variety of substituted isoquinolines have been synthesized in good to excellent yields by the electrophilic ring closure of iminoalkynes in the presence of various external electrophiles. The best results were obtained with •an excess of the electrophile, plus 3 equiv of sodium bicarbonate as a base when needed, at room temperature with either acetonitrile or methylene chloride as the solvent. This electrophilic ring closure is highly effective when an aryl-or alkenyl-substituted alkyne is utilized. Other acetylenes fail to undergo this ring closure. Mono-substituted isoquinolines have been prepared in good to• excellent yields by the silver-catalyzed cyclization of various iminoalkynes. The best results were obtained using 5 mol % silver nitrate at 50 °C in chloroform. Aryl-, vinylic-, and alkyl-substituted iminoalkynes undergo this. silver-catalyzed cyclization in excellent yields.

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