Beijing 10094, China
Introduction
Pyrazolidine and pyrazoline are highly important compounds due to their
widely existence in natural products, bioactive and unique photophysical
properties. 1–13 Therefore, many experimental and theoretical works
have been dedicated to the efficient and stereoselective synthesis of
pyrazolidine and pyrazoline compounds. 14–28 For instance, Kobayashi
found that the Lewis acid chiral zirconium/BINOL complexes can be used
as an efficient catalyst to synthesis en- tioselective pyrazolidine
products via inter or intramolecular [3+2] cycloaddition between
hydrazone and alkenes.22–24 Müller and List, however, using a chiral
Brønstedacid to generate enantiopure pyrazolidine derivative. 14 Later
on, Rueping’s group provides a more general and enantioselective
Ntriflylphosphoramide catalyst for the intermolecular [3+2]
cycloaddition between hydrazones and alkenes. 27 Houk et al. further
employed experimental study and computational calculations to elucidate
the mechanism of the Ntriflylphosphoramide catalyzed [3+2]
cycloaddition between hydrazones and alkenes. 21