Gold-Catalyzed Synthesis of Pyrroles and Furans

Significance

Reported is an efficient and rapid synthesis of furans 2a and pyrroles 2b from readily available 3-alkyne-1,2-diols 1a and amino-3-alkyn-2-ols 1b under combined gold and silver catalysis. Interestingly, the intramolecular cyclization fails when gold and silver compounds alone are used. The optimized conditions were applied to various alkynyldiols 1a using [(PPh₃)AuCl-AgNTf₂] for the synthesis of furans 2a and amino-3-alkyn-2-ols 1b using [(PPh₃)AuCl-AgNOTf] for the preparation of di- and monosubstituted pyrroles 2b. The reaction is suggested to proceed via a coordination of the acetylene bond to cationic gold species (enhancing the electrophilicity) followed by a 5-endo cyclization and finally dehydration. It was observed that the reactivity of the diastereoisomers (syn- and anti-3) is slightly different.