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.