Molybdenum-Catalyzed Allylic Substitution in Glycals: A C-C Bond-Forming Ferrier-Type Reaction

The mild, Lewis-acidic complexes [Mo(CO)4Br2]2, (MeCN)2Mo(CO)3(SnCl3)Cl, and (acac)2Mo(OTf)2 have been found to catalyze the C(1)-specific C-glycosylation reaction of glycal acetates 1-3 with silyl enol ethers 4a-4c and electron-rich aromatics 5a, 5b (PhOMe, PhOH). While silyl enol ethers produce predominantly α-C-glycopyranosides (with 2 : 1 to 4 : 1 selectivity), aromatics tend to afford mainly β-C-glycopyranosides (2 : 1 to 3 : 1) in a thermodynamically controlled process.