1,4-Diazabicyclo[2.2.2]octane Bis(sulfur dioxide) Adduct (DABSO)

Introduction

1,4-diazabicyclo[2.2.2]octane bis (sulfur dioxide) adduct (DABSO)[1] consists of a 1:2 complex of DABCO with sulfur dioxide. This reagent has recently found various applications, such as sulfonamide formation via palladium coupling or synthesis of sulfonylureas. It is a colorless, stable, yet hygroscopic powder and it is more convenient to handle and safer than gaseous sulfur dioxide. In addition, the health and safety regulations concerning the transportation and storage of gaseous sulfur dioxide make DABSO even more useful. However, DABSO is an expensive commercially available reagent, generally sold only in gram-scale amounts, currently produced by few chemical suppliers. Its preparation is described in the literature using gaseous sulfur dioxide which is condensed or bubbled through a solution of DABCO. This procedure uses a large excess of toxic sulfur dioxide, which should be trapped to avoid discarding in the atmosphere. As a surrogate for SO₂, DABSO can be used to form sulfonyl derivatives following two different pathways: either starting from aryl halides under palladium catalysis, or with a C- or N-nucleophile in the presence of an oxidizing agent.

Scheme 1 Synthesis of 1,4-diazabicyclo[2.2.2]octane bis (sulfur dioxide) adduct (DABSO)

• References

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