Synthesis of isoquinolones by visible-light-induced deaminative [4+2] annulation reactions

Herein a metal-free approach for the synthesis of isoquinolone derivatives by means of photoinitiated deaminative [4+2] annulation of alkynes and N-amidepyridinium salts is described. This protocol exhibits a broad scope and good functional group tolerance and regioselectivity under benign reaction conditions. Preliminary studies suggest that the critical amide radical is derived from the photocatalytic cleavage of the N-N bond of the N-amidepyridinium salt, which adds to the triple bond of the alkyne and undergoes the annulation process to afford the desired isoquinolones.