I₂-Promoted <i>gem</i>-Diarylethene Involved Aza-Diels–Alder Reaction and Wagner–Meerwein Rearrangement: Construction of 2,3,4-Trisubstituted Pyrimido[1,2-<i>b</i>]indazole Skeletons

Abstract

A [3 + 1 + 2] cyclization-rearrangement reaction scheme was developed to synthesize pyrimido[1,2-<i>b</i>]indazoles from aryl methyl ketones, 3-aminoindazoles, and <i>gem</i>-diarylethenes. This metal-free process proceeds via a sequential aza-Diels-Alder reaction and Wagner-Meerwein rearrangement, and a possible reaction mechanism was demonstrated based on control experiments. This method exhibits good substrate compatibility and allows simple reaction conditions. Moreover, the products display significant aggregation-induced emission characteristics after simple modifications.