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Synthesis | Organic Synthesis | Newman-Kwart Rearrangement

The Newman-Kwart rearrangement (NKR) is a well-established and powerful synthetic technique for converting phenols into corresponding thiophenols via their thiocarbamates. It represents a robust and reliable reaction under various conditions for synthesizing valuable products for medicinal and agrochemical purposes.

Introduction

Not only thiophenols, but even other sulfur-containing functional groups can be accessed by this method, such as thioesters, sulfoxides or sulfonic acids.

Thus, the NKR can be used to generate particular aromatic substitution patterns, making it a valuable procedure in several synthetic disciplines like medicinal chemistry, dye generation, agrochemical production, and even supramolecular chemistry.

However, the key O- to S-aryl migration has a high activation energy. Therefore, several examples of the NKR proceed only at high temperatures significantly above 200°C, even up to 300°C.

These characteristics make the NKR prone to microwave mediation, as reaching such high temperatures under classical conditions is usually toilsome and time-consuming. Initial results showed satisfactory performance of this reaction under microwave irradiation at small scale, thus it was of interest to further investigate the microwave-assisted scale-up potential for the NKR.

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