Pyrrolidine-oxadiazolone
based organocatalysts are envisaged, synthesized, and utilized for
asymmetric Michael reactions. Results of the investigations suggest
that some of the catalysts are indeed efficient for stereoselective
1,4-conjugated Michael additions (dr: >97:3, ee up to 99%) in high
chemical yields (up to 97%) often in short reaction time. As an extension,
one enantiopure Michael adduct has been utilized to synthesize optically
active octahydroindole.
Organic
transformations exclusively in water as an environmentally
friendly and safe medium have drawn significant interest in the recent
years. Moreover, transition metal-free synthesis of enantiopure molecules
in water will have a great deal of attention as the system will mimic
the natural enzymatic reactions. In this work, a new set of proline-derived
hydrophobic organocatalysts have been synthesized and utilized for
asymmetric Michael reactions in water as the sole reaction medium.
Among the various catalysts screened, the catalyst 1 is
indeed efficient for stereoselective 1,4-conjugated Michael additions
(dr: >97:3, ee up to >99.9%) resulting in high chemical yields
(up
to 95%) in a very short reaction time (1 h) at room temperature. This
methodology provides a robust, green, and convenient protocol and
can thus be an important addition to the arsenal of the asymmetric
Michael addition reaction. Upon successful implementation, the present
strategy also led to the formation of an optically active octahydroindole,
the key component found in many natural products.
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