Asymmetric Synthesis of Chiral Dihydrothiopyrans via an Organocatalytic Enantioselective Formal Thio [3 + 3] Cycloaddition Reaction with Binucleophilic Bisketone Thioethers

An unprecedented organocatalytic highly enantioselective approach
to a 3,4-dihydro-2H-thiopyran scaffold with two contiguous
stereogenic centers has been implemented through a formal thio [3
+ 3] cycloaddition process involving a Michael–aldol condensation
cascade sequence. Notably, a new class of binucleophilic bisketone
thioethers is designed for the process. Furthermore, the fine-tuning
of their reactivity enables the cascade process to proceed with highly
regioselectively.