Core Scaffold-Inspired Stereoselective Synthesis of Spiropyrazolones via an Organocatalytic Michael/Cyclization Sequence

Herein, the organocatalytic asymmetric Michael/cyclization
sequence
of α-isothiocyanato imides and esters with a variety of unsaturated
pyrazolones is presented, in general, affording functionalized spiropyrazolones
containing three contiguous stereogenic centers in high levels of
diastereo- and enantioselectivity (up to 20:1 dr and 99% ee). Moreover,
the current protocol provides a highly efficient and convenient strategy
that allows rapid enantioselective construction of diversely spiropyrazolone
skeletons with high optical purity.