Divergent Synthesis of Oxazole and Oxazoline Derivatives by Tandem (3+2) Cyclization-Isomerization Reactions between Aldehydes and Vinylogous Isocyano Esters.

The utility of underexplored vinylogous isocyano esters in the synthesis of oxazole derivatives is demonstrated herein. A divergent base-promoted tandem (3+2) cyclization-isomerization reaction with aldehydes divergently yields bisubstituted oxazoles (up to 90% in MeOH with 2 equiv of DBU) or oxazolines (up to 80% in CH2Cl2 with 1 equiv of DBU) A density functional theory (DFT) study of these reactions supports the experimental evidence, confirming the mechanism and selectivity of this divergent process.