Silver(I)-Catalyzed Tandem Reaction of Enynones and 4-Alkenyl Isoxazoles: Synthesis of 2-(Furan-2-yl)-1,2-dihydropyridines

Silver-(I)-catalyzed tandem reaction of enynones with4-alkenylisoxazoles provides access to 2-(furan-2-yl)-1,2-dihydropyridines.No competitive cyclopropanation of alkenes and O-H insertionvia (2-furyl)-carbene complexes were observed. The cascade reactionproceeds via the formation of (2-furyl)metal carbene intermediate,the N-O bond cleavage of 4-alkenyl isoxazoles/rearrangement,subsequent 6 pi electrocyclic reaction, and [1,5] H-shift. Thesuccessive construction of both 1,2-dihydropyridine skeleton and furanframe has been achieved in the one-pot reaction. A broad range ofreadily available enynones and 4-alkenyl isoxazoles are suitable tothis protocol; however, when R-3 is the alkyl group suchas n-Bu and Me, a complicated mixture was generatedwithout the desired products. In addition, in the case of R-4 = bulky group such as R-3 (SiOCH2)-Si-', the reaction gave an in situ oxo-product of (2-furyl)-silvercarbene. An atom-economic strategy for the synthesis of 2-(furan-2-yl)-1,2-dihydropyridineshas been established.