Method for Introducing Sulfur Linkages

By: Josephine Nakhla, Chemfiles Volume 10 Article 3

Matzger and co-workers developed a useful method for the introduction of sulfur linkages using Bu3SnSSnBu3 in the preparation of oligothienoacenes. Historically, the preparation of these molecules has been limited and not feasible for longer chain thienoacenes. The low solubility and problematic isolation both contribute to the challenges associated with preparing oligothienoacenes. The synthesis of these molecules in the Matzger lab begins with the introduction of the TIPS group through Li-Br exchange of the precursor dibromide and addition of TIPS-Cl. The bromine at the 2-position was treated with LDA to provide the 3-bromo-substitued isomer. The use of Bu3SnSSnBu3 in a Pd-catalyzed coupling with 2 equivalents of the 3-bromo-substituted precursor provided the thio-linked thienoacene. Incorporating the sulfur linkage typically involves metalation followed by reaction with bis(phenylsulfonyl)sulfide, which often leads to linking at the two- and three-position rather than the 3,3-position. Oxidative ring closure and deprotection yields the final oligothienoacene (Scheme 4). The TIPS groups are strategically placed to avoid competing deprotonation at the 2-position when conducting the oxidative ring closure.


Scheme 4. Preparation of oligothienoacenes using Bu3SnSSnBu3 to introduce sulfur linkage

Scheme 4. Preparation of oligothienoacenes using Bu3SnSSnBu3 to introduce sulfur linkage (720585)

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Materials

     

References

  1. Zhang, X.; Cote´, A. P.; Matzger, A. J. J. Am. Chem. Soc. 2005, 127, 10502.

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