Enantioselective Construction of Spiro[indoline-3,2′-pyrrole] Framework via Catalytic Asymmetric 1,3-Dipolar Cycloadditions Using Allenes as Equivalents of Alkynes

The first catalytic asymmetric 1,3-dipolar cycloadditions (1,3-DCs) of isatin-derived azomethine ylide with allenes have been established, which efficiently assembly isatins, amino-esters and 2,3-allenoate into enantioenriched spiro[indoline-3,2'-pyrrole] derivatives with a quaternary stereogenic center in generally high enantioselectivities (80-98% ee). In this allene-involved 1,3-DC, an unexpected spirooxindole framework bearing an intra-annular C═C double bond was generated, which is quite different from previously reported 1,3-DCs of allenes. This approach not only confronted the great challenge in using allenes as dipolarophiles of 1,3-DCs, but also provided a unique strategy of using allenes as equivalents of alkynes to construct spiro[indoline-3,2'-pyrrole] structure. Besides, this reaction also represents the first catalytic asymmetric ketone-involved 1,3-DCs of allenes, which will also greatly enrich the research contents of 1,3-DCs, the chemistry of allenes as well as the synthetic methods of spirooxindoles.