Sulfonyl-1,2,3-Triazoles: Convenient Synthones for Heterocyclic Compounds

1-Sulfonyl-1,2,3-triazoles, which are readily available through copper-catalyzed azide-alkyne cycloaddition, are stable precursors to Rh–azavinyl carbenes, as well as carbene complexes of other metals. Among other transformations, these reactive intermediates can be used for the introduction of a nitrogen atom into various heterocycles that are important in both synthetic and medicinal chemistry. Carbenes generated from diazocarbonyl compounds 1 are known to react with carbonyl groups to produce ylides 2, which usually react in subsequent 1,3-dipolar cycloadditions to access complex structures [Eq. (1)]. Herein, we report that Rh–azavinyl carbenes react with aldehydes to give adducts that undergo an intramolecular cyclization instead of a 1,3-dipolar cycloaddition. This transformation results in homochiral 3-sulfonyl-4-oxazolines 4 [Eq. (2), left], which are produced in excellent yield and with high enantioselectivity. These sparsely studied compounds contain an easily installed stereocenter and a synthetically useful electron-rich double bond.