Probing the Efficiency of N-Heterocyclic Carbene Promoted O- to C-Carboxyl Transfer of Oxazolyl Carbonates
摘要:
Screening of a range of azolium salts, bases and solvents for reactivity indicates that triazolinylidenes, generated in situ with KHMDS in THF, promote the Steglich rearrangement of oxazolyl carbonates with high catalytic efficiency (typical reaction time 5 min at < 1.5 mol % NHC). This protocol shows wide substrate applicability, even allowing the efficient generation of vicinal quaternary centers. An improved experimental procedure is also described that allows a simplified one-pot reaction protocol to be employed with similarly high catalytic efficiency.
Efficient N-Heterocyclic Carbene-Catalyzed O- to C-Acyl Transfer
摘要:
An N-heterocyclic carbene promotes the rearrangement of alpha-amino acid derived O-acyl carbonates to their corresponding C-acylated isomers, generating a C-C bond and a quaternary stereocenter with high efficiency, under mild reaction conditions and with low catalyst loadings.
Enantioselective Construction of Quaternary Stereocenters: Rearrangements of <i>O</i>-Acylated Azlactones Catalyzed by a Planar-Chiral Derivative of 4-(Pyrrolidino)pyridine