Electrochemically Mediated Oxidative Transformations of Substituted 4-Methoxystilbenes: Effect of Ortho-Substituted Nucleophilic Groups

Abstract

A systematic study was undertaken to determine the influence of ortho'-substituted nucleophilic groups (OH, NH, or NHR) on the reactivity of anodically generated 4-methoxy- and 3,4-dimethoxystilbene cation radicals. The results showed that when ortho-substituted nucleophilic groups such as OH and NHR are present in the other ring, both direct and crossover intramolecular cation-nucleophile reactions occur to give bisbenzofurans/bisindoles or fused bisbenzopyrans/bisquinolines, respectively. Where an additional 3-methoxy substituent is present, bridged oxocine/azocine products are formed in addition to the bisbenzopyrans/bisquinolines and bisbenzofurans/bisindoles. Mechanistic rationalization of the observed behavior is presented based on a generalized pathway involving fast cation radical dimerization following electron transfer, followed by direct and crossover trapping of the benzylic cations by the ortho-substituted oxygen and nitrogen nucleophilic groups. In the instances where an additional 3-methoxy group is present, the bridged oxocine/azocine products are also formed as a result of competing aromatic substitution (Friedel-Crafts reaction). The results have shed further light and provided additional clarification on the reactivity of anodically generated stilbene cation radicals.

Synthetic Organic Electrochemical Methods Since 2000: On the Verge of a Renaissance

“…Kam and co-workers carried out extensive studies on the oxidative dimerization of stilbenes under constant potential conditions. 494,495 The reaction outcomes were strongly influenced by the choice of solvent (Figure 32C). [3 + 2] and [4 + 2] adducts were obtained in MeCN with the former favored after an aqueous workup.…”

Electrochemical Dimerization of Phenylpropenoids and the Surprising Antioxidant Activity of the Resultant Quinone Methide Dimers

“…Several reports have demonstrated the utility of anodic oxidation in total synthesis, but efforts to apply this approach in the context of phenylpropenoid natural product total synthesis have been limited by low yields and lack of regiocontrol . Here, we present an electrochemical method for the regioselective dimerization of various hydroxystilbene derivatives (Figure B).…”

Hypervalent Iodine(III)-Catalyzed Synthesis of 2-Arylbenzofurans

“…Light-yellow solid; yield: 184 mg (72%); mp 135-137 °C (Lit. 30 Yellow oil). IR (KBr): 760, 840, 954, 1020, 1085, 1161, 1230, 1370, 1510, 1611, 1750, 3369 cm -1 .…”