Stereospecific Syntheses of Enaminonitriles and β‑Enaminoesters via Domino Ring-Opening Cyclization (DROC) of Activated Cyclopropanes with Pronucleophilic Malononitriles

Two novel synthetic protocols for
the syntheses of highly functionalized
five-membered carbocyclic enaminonitriles and β-enaminoesters
have been developed via domino ring-opening cyclization (DROC) and
DROC/decarboxylative tautomerization of activated cyclopropanes with
malononitrile pronucleophiles, respectively. Both of the efficient
strategies (yield up to 93%) have been generalized with various donor–acceptor
and acceptor cyclopropanes as well as with malononitrile derivatives.
The stereospecific variants of the two SN2-type DROC strategies
have also been developed by employing enantiopure donor–acceptor
(DA) cyclopropanes to synthesize the corresponding nonracemic products
with excellent stereoselectivities (dr up to >99:1, ee up to >99%).