MeOPEG-Supported Carbene Catalysts

Significance

Preparation of MeOPEG resin-supported heteroazolium salts and their catalytic activities are described. Thus, heteroazoles 1 reacted with propargyl bromide to give the heteroazolium salts 2 quantitatively. Treatment of 2 with MeOPEG-supported azide in the presence of CuBr and ascorbic acid in a mixed solvent of H₂O and t-BuOH afforded the desired MeOPEG resin-supported heteroazolium salts 3 (eq. 1). The intramolecular Stetter reaction of 4 with 3a in the presence of DIPEA gave chloman-4-one 5 in 84% yield (eq. 2). The reductive esterification of 3-phenyl-2-propynal 6 was carried out in the presence of 3b, DMAP, and ethanol to afford ethyl cinnamate 7 in 83% yield (E/Z > 95:5) (eq. 3).