Palladium-catalyzed enantioselective decarboxylation of vinyl cyclic carbamates:Generation of amide-based aza-1,3-dipoles and application to asymmetric 1,3-dipolar cycloaddition

The catalytic asymmetric dipolar cycloaddition reaction is efficient for the construction of various chiral valuable carbo-and heterocycles.Thus,the design and exploration of new dipoles and the subsequent control of their reactivity for various stereoselective cycloadditions are significant aspects of modern organic synthesis.Herein,we have developed a series of vinyl cyclic carbamates containing an oxazolidine-2,4–dione fragment and used them as reactive precursors for in situ generation of amide-based aza-π-allylpalladium 1,3-dipoles,which could be applied to asymmetric decarboxylative 1,3-dipolar cycloaddition with different types of dipolarophiles containing C=C,C=N,and C=O double bonds.This strategy provides an opportunity for the synthesis of previously unusual structures,such as highly functionalized optically pure pyrrolidin-2-ones,imidazolidin-4-ones,and oxazolidin-4-ones.This protocol also has significant features including wide substrate scope,mild reaction conditions,simple operation,and good to excellent results(70 examples,up to 99%yield,>20:1 dr and 99%ee).This unique method significantly expands the reaction range of the amide-based aza-π-allylpalladium 1,3-dipoles compared to the precedents.

DBU-catalyzed dearomative annulation of 2-pyridylacetates withα,β-unsaturated pyrazolamides for the synthesis of multisubstituted 2,3-dihydro-4H-quinolizin-4-ones

The reaction of 2-pyridylacetates andα,β-unsaturated pyrazolamides with DBU as the catalyst has been developed.A range of unexplored multisubstituted 2,3-dihydro-4H-quinolizin-4-ones are obtained with satisfactory yields(up to 94%)and excellent diastereoselectivities(all cases>20:1 dr)via a dearomative[3+3]annulation process.This practical method also features transition metal free,mild reaction conditions,wide functional group tolerance,easy scale-up synthesis,and versatile further derivatization.