Enone–Alkyne Reductive Coupling: A Versatile Entry to Substituted Pyrroles
摘要:
The reductive coupling of enones or enals with alkynes, followed by olefin oxidative cleavage and Paal-Knorr cyclization, provides a versatile entry to a variety of pyrrole frameworks. A number of limitations of alternate entries to the requisite 1,4-dicarbonyl intermediate are avoided. Classes of pyrroles that are accessible by this approach include 2,3-, 2,4-, 1,2,3-, 1,2,4-, 2,3,5-, and 1,2,3,5-substituted monocyclic pyrroles as well as a number of fused-ring polycyclic derivatives.
derivatives are also obtained by the reaction of α-bromooximes with vinyl ethers and silyl enol ethers in the presence of Na2CO3. Dihydro-1,2-oxazines can be converted into pyrrole derivatives viareductivedeoxygenation by treating with Fe3(CO)12 in moderate to excellent yields. Iron carbonyl complexes other than Fe3(CO)12 are also effective for the pyrrole-forming reaction. The efficiency of the complexes
An Au(i)-catalyzed tandem reaction, involving a Meyer–Schuster rearrangement/1,2-migration/Paal–Knorr cyclization cascade has been successfully developed.
The reaction of 5,6-dihydro-4H-1,2-oxazines, which are derived from α-bromooximes and enamines, with ironcarbonylcomplexes such as Fe3(CO)12 and (C2H5)3NH[HFe3(CO)11] gives pyrrole derivatives in high yields, accompaning deoxygenation from the oxazines. The pyrroles are also obtained by an one-pot reaction using α-bromooximes, enamines and ironcarbonyls.