Recent advances in the Newman–Kwart rearrangement

Since its independent development by Newman and Kwart in the 1960s, the Newman–Kwart rearrangement has been extensively studied for synthesizing thiophenols. A major limitation of this reaction is the requirement for high temperatures. However, recently developed methods have significantly improved its synthetic utility. The method developed by Lloyd-Jones et al., which employs a Pd catalyst, successfully lowered the reaction temperature to around 100 °C by utilizing a reaction mechanism that proceeds via oxidative addition of the CO bond of O-aryl thiocarbamates. The single-electron oxidation approach introduced by Nicewicz et al. enabled the Newman–Kwart rearrangement to proceed at room temperature and significantly expanded its substrate scope. This strategy, based on the generation of electrophilic thiyl radical intermediates, was further extended to the development of Newman–Kwart rearrangement protocols using Ce or Fe oxidants, as well as electrochemical approaches. More recently, a reaction system employing a Bi catalyst has been developed to facilitate the Newman–Kwart rearrangement of O-heteroaryl thiocarbamates at room temperature. This paper provides an overview of the recent advances in this field.