Newman–Kwart rearrangement

The Newman–Kwart rearrangement is a type of rearrangement reaction in which the aryl group of an O-aryl thiocarbamate, ArOC(=S)NMe₂, migrates from the oxygen atom to the sulfur atom, forming an S-aryl thiocarbamate, ArSC(=O)NMe₂. The reaction is named after its discoverers, Melvin Spencer Newman and Harold Kwart.

The Newman–Kwart rearrangement is one of the most important ways of synthesising thiophenols. A phenol (1) is deprotonated with a base such as DABCO or NaH and reacted with a thiocarbamoyl chloride (2) to form an O-aryl thiocarbamate (3). Heating 3 to around 250 °C causes it undergo Newman–Kwart rearrangement to an S-aryl thiocarbamate (4). Alkaline hydrolysis or similar cleavage yields a thiophenol (5).