Sustainable methine sources for the synthesis of heterocycles under metal- and peroxide-free conditions†
Alcohols and ethers were identified as sustainable methine sources for synthesizing quinazolinone and benzimidazole derivatives using a combination of TsOH·H2O/O2 and appropriate bis-nucleophiles for the first time. Deuterium labeling studies clearly proved that the C2 hydrogen of the synthesized heterocycles came from the methine source. These unique reaction conditions were successfully applied to the synthesis of echinozolinone (2e′), 2f′ (a common precursor of rutaecarpine and (±) evodiamine), and dimedazole (6d). Notable features of this method include its low toxicity, use of commercial feedstocks as substrates, low cost, broad functional group tolerance and suitability for a wide range of bis-nucleophilic starting materials.