Thioacetals can be useful protecting groups and key intermediates in organic synthesis. However, their synthesis usually involves thiols or dithiols, which have a very unpleasant odor. Alternative approaches either suffer from hard-to-remove byproducts or expensive reagents.
Dhanarajan Arunprasath and Govindasamy Sekar, Indian Institute of Technology, Madras, have used a carbene insertion reaction across sulfur-sulfur and selenium-selenium bonds to synthesize thioacetals and selenoacetals without a need for thiols or selenols. The team used N-tosylhydrazones as carbene precursors, which were converted to intermediate diazo compounds with a base (KOtBu). Loss of N2 then generates a carbene, which can react with the S–S bond of disulfides or the Se–Se bond of diselenides. A final rearrangement gives the desired thio- or selenoacetal.
The reaction allows the synthesis of a wide range of thio- and selenoacetals in good yields and with short reaction times using a stable and safe carbene precursor.
- A Transition-Metal-Free and Base-Mediated Carbene Insertion into Sulfur-Sulfur and Selenium-Selenium Bonds: An Easy Access to Thio- and Selenoacetals,
Dhanarajan Arunprasath, Govindasamy Sekar,
Adv. Synth. Catal. 2016.