Direct Synthesis of a Nitrogen-Containing Eight-Membered Cyclic Alkyne from a Linear Alkyne and Its Reactivity

Eight-membered cyclic alkyne <b>3</b> was synthesized from <b>1</b>, bearing an <i>N</i>-tosyl-<i>o</i>-alkynylanilide and alkyl bromide, by a high-temperature treatment in the presence of a base. This is the first example of the direct synthesis of an eight-membered cyclic alkyne containing a nitrogen atom from the corresponding linear alkyne. The structural requirements for this cyclization were also investigated. Eight-membered cyclic alkyne <b>3</b> reacted with benzyl azide without a copper(I) salt to give triazoles <b>17</b> and <b>18</b> at room temperature.