NHC And Br?nsted Base-Catalyzed Annulation Of Catalytic Alkynyl 1,2-Diketones

The umpolung of alkynyl 1,2-diketones via N-heterocyclic carbene(NHC)catalysis was achieved for the first time,allowing rapid access to a large variety of synthetically and pharmaceutically important ?-pyrones under very mild conditions.A completely new NHC-catalyzed umpolung pattern involving an O-acylated allenolate as the key intermediate was proposed.Moreover,an unprecedented reaction pathway,featured by a series of group migrations and new bond formation,was postulated to demonstrate the formation of the products.On the basis of first work,we continued our research for alkynyl 1,2-diketones.The discovery of new reaction modes mediatd by easily available substrates is an important research topic in organic synthesis.Allyl ketone and related compounds have been demonstrated to undergo ?-or ?-selective additions to different electrophiles.We disclosed here the Br?nsted base-catalyzed reaction of allyl ketones and alkynyl 1,2-diketones,which underwent a unique ?-selective addition/intramolecular aldol-type annulation/C-C bond cleavage process,and a series of 2-acyloxycyclopent-3-enones could be obtained under very mild conditions.Cyclopentadienones(CPDs)are a family of fascinating molecules with broad applications.For instance,they have been used in annulation reactions to release aromatic rings with multiple substituents,and employed as ligands to form a range of coordination complexes.Furthermore,cyclopentadienones have been used to make biologically active natural products,and devices.Here we reported a new protocol allowing the access to trisubstituted CPDs from ?-acyloxy-?,?-unsaturated cyclic ketones.Noteworthy was that such type of starting substrates can be synthesized in one step using our recently developed method under particularly mild conditions,and all substituents can be changed at will.Furthermore,the reaction displays excellent regioselectivity in Diels-Alder reactions.