Intramolecular <i>ipso</i>-Halocyclization of 4-(<i>p</i>-Unsubstituted-aryl)-1-alkynes Leading to Spiro[4,5]trienones: Scope, Application, and Mechanistic Investigations

A new, general method for the synthesis of spiro­[4,5]­trienones is described by the intramolecular ipso-halocyclization of 4-(p-unsubstituted-aryl)-1-alkynes. In the presence of halide electrophiles, a variety of 4-(p-unsubstituted-aryl)-1-alkynes underwent the intramolecular ipso-halocyclization with water smoothly, affording the corresponding halo-substituted spiro­[4,5]­trienones in moderate to good yields. The obtained spiro­[4,5]­trienones can be applied in constructing the azaquaternary tricyclic skeleton via Pd-catalyzed Heck reaction. Notably, the prepared spiro­[4,5]­trienones and azaquaternary tricycles are of importance in the areas of pharmaceuticals and agrochemicals. The mechanism of the intramolecular ipso-halocyclization reaction is also discussed according to the 18O-labeling experiments and DFT calculations.