Isothiourea-Mediated Asymmetric O- to C-Carboxyl Transfer of Oxazolyl Carbonates: Structure-Selectivity Profiles and Mechanistic Studies

The structural motif within a series of tetrahydropyrimidine‐based isothioureas necessary for generating high asymmetric induction in the asymmetric Steglich rearrangement of oxazolyl carbonates is fully explored, with crossover and dynamic 19F NMR experiments used to develop a mechanistic understanding of this transformation. As easy as O to C: The ability of a series of tetrahydropyrimidine‐based isothioureas to promote the asymmetric Steglich reaction has been evaluated (see scheme). Good to excellent levels of enantioselectivity were generally observed for the rearrangement of oxazolyl carbonates, with markedly different catalytic efficiencies observed with variation of the stereodirecting group(s). Crossover and dynamic 19F NMR experiments were also used to develop a mechanistic understanding of this transformation.