A modified all-in-one DMSO-activating and base releasing reagent for the Parikh-Doering-type benzylic oxidation reaction

The Parikh-Doering reaction (PDR), an example of a DMSO-mediated oxidation, finds use in natural product synthesis when mild oxidative reaction conditions are required. The original PDR conditions require the use of Py-SO3, NEt3, and DMSO, in DCM. As part of our ongoing interest in sulfating agents, we recently disclosed the novel structure of tributylsulfoammonium betaine (TBSAB) that has a formal N-S bond. Herein, we explore a commercial sulfating agent, triethylamine-sulfur trioxide complex, as an all-in-one sulfation and base releasing reagent for a modified PDR. Single crystal X-ray crystallography confirmed for the first time that triethylamine-sulfur trioxide complex exists as a triethylsulfoammonium betaine (TESAB). A range of primary and secondary alcohols were screened for competency with TESAB. Reactivity was observed for the first time with i) a non Py-SO3 sulfating agent and ii) without the need for external base additives. Moderate to good yields of aldehydes and ketones can be prepared in an atom-efficient manner with TESAB and without the need to separate toxic pyridine impurities.