MgO-Promoted [4 + 2] Cyclization Using HFA·3H 2 O/SOCl 2 /PPh 3 : Modular Synthesis of gem -Bis(trifluoromethyl)dihydrothiopyrans

The present study reports an unprecedented [4 + 2] annulation for the modular synthesis of gem -bis(trifluoromethyl)-3,6-dihydro-2 H -thiopyrans. The transformation employs readily available HFA·3H 2 O and SOCl 2 as a convenient (CF 3 ) 2 C═S surrogate in the presence of PPh 3, with MgO promoting the subsequent thia -Diels–Alder reaction of 1,3-dienes. The method features a broad substrate scope, excellent practicality for gram-scale synthesis and late-stage functionalization of biologically active molecules, as well as versatile product derivatization. Mechanistic studies identify hexafluoroisopropyl polysulfide species as key intermediates in this process.