Sulfur Dioxide Insertion Reactions for Organic Synthesis

In the context of increasing attention to sustainable and green chemistry, a variety of efforts have been devoted to atom economical and environmentally friendly methods to construct complex molecules. The incorporation of sulfur dioxide into small molecules is an attractive and promising strategy since it introduces the sulfonyl moiety from simple and readily available sources. Developing sulfur dioxide insertion reactions for organic synthesis has become an active research area in the last few years, particularly owing to the development of innocuous and bench-stable sulfur dioxide surrogates. In this chapter, we will highlight the importance of sulfonyl groups (—SO₂—) in diverse fields, introduce the basic properties of sulfur dioxide, and classify the reaction types derived from sulfur dioxide. We will also present the main contents and emphases of this book, and wish to give a comprehensive understanding of sulfur dioxide insertion chemistry to the readers.

The most significant driving force in the field of sulfur dioxide insertion has been the development of safe and bench-stable sulfur dioxide surrogates. To date, several sulfur dioxide surrogates have been developed and proved to be efficient in the processes of sulfur dioxide insertion. Among them, DABCO·(SO₂)₂ (named DABSO) and potassium metabisulfite (K₂S₂O₅) are two of the most commonly used sulfur dioxide surrogates, which have been identified and documented in various transformations. In this chapter, we will introduce these sulfur dioxide surrogates, with an emphasis on those utilized in sulfur dioxide insertion reactions.

The area of sulfur dioxide insertion reactions has entered a new stage of renaissance in the last several years. In this chapter, we will summarize the reactions involved with the insertion of sulfur dioxide, with an emphasis on recent advances achieved by the application of sulfur dioxide surrogates. We will describe representative examples following the ideas of reaction design, and present the general experimental procedures. According to the types of transformation, these reactions are classified into four parts: (i) nucleophilic addition with organometallic reagents; (ii) transition metal catalysis; (iii) free radical reactions; and (iv) pericyclic reactions. These processes provide an efficient and practical route for the construction of sulfonyl-containing compounds.

The above three chapters have overviewed the versatilities of sulfur dioxide in organic synthesis and described the commonly utilized sulfur dioxide surrogates. We classified and discussed the transformations in detail involving insertion of sulfur dioxide, with an emphasis on the reaction design and mechanisms, revealing the valuable insights of sulfur dioxide insertion reactions. In this chapter, we will summarize the book and look into the future of sulfur dioxide chemistry. We hope this book will help readers to review the field of sulfur dioxide chemistry, and ignite the interest of readers to solve the existing challenges and exploit new areas of sulfur dioxide chemistry.