Greener Preparation of 5-Ethyl-4a-hydroxyisoalloxazine and Its Use for Catalytic Aerobic Oxygenations

Isoalloxazine ring systems are found in flavin cofactors in nature, and the simulation of their redox catalyses is an important task for developing sustainable catalytic oxidation reactions. Although 5- ethyl-4a-hydroxyisoalloxazines are among the most promising candidates as catalyst for such purposes, the use of them for laboratorial as well as industrial synthetic chemistry has so far been quite limited presumably due to the lack of their preparation methods readily, safely, and inexpensively available. In this communication, we introduce an environmentally benign and practical preparation of 5-ethyl-4a-hydroxy-3,7,8,10-tetramethylisoalloxazine (1EtOH) from 3,7,8,10-tetramethylisoalloxazine (1), in which conventional synthetic requirements, including (i) operations under inert conditions, (ii) risky or expensive chemicals, and (iii) isolation of labile intermediates, have all been dissolved. In addition, we have presented that 1EtOH could be an effective catalyst for Baeyer-Villiger oxidation as well as sulfoxidation with molecular oxygen (O2) as a terminal oxidant under suitable conditions, which is the first report on aerobic oxygenations catalyzed by 5-alkyl-4a-hydroxyisoalloxazines.

This is the peer-reviewed version of the following article: Oonishi, T. , Kawahara, T. , Arakawa, Y. , Minagawa, K. and Imada, Y. (2019), Greener Preparation of 5‐Ethyl‐4ahydroxyisoalloxazine and Its Use for Catalytic Aerobic Oxygenations. Eur. J. Org. Chem., 2019: 1791-1795, which has been published in final form at https://doi.org/10.1002/ejoc.201801865. This article may be used for non-commercial purposes in accordance with Wiley-VCH Terms and Conditions for Self-Archiving.