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

The Parikh-Doering reaction, an example of the series of DMSO-mediated selective oxidation named reaction family, finds ongoing use in natural product synthesis when mild oxidative reaction conditions are required. The original conditions require the use of Py-SO3 and NEt3 along with DMSO and 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 (not dative) and may indicate that other N(sp3) amine-SO3 complexes have been misassigned. Herein, we explore a commercial sulfating agent, triethylamine-sulfur trioxide complex, as an all-in-one sulfation and base releasing reagent for a modified Parikh-Doering reaction. Single crystal X-ray crystallography further confirms our hypothesis than triethylamine-sulfur trioxide complex exists as triethylsulfoammonium betaine (TESAB). Employing TESAB as an all-in-one reagent, a range of primary and secondary alcohols were screened for competency. Reactivity was observed for the first time with 1) a non Py-SO3 sulfating agent and 2) without the need for additional base. Moderate to good yields of aldehydes and ketones can be prepared in an atom-efficient improvement with concomitant removal of toxic pyridine by-products.