Background:
Since the discovery of metal-free catalysts or organocatalysts about twenty years ago, a number
of small molecules with different structures have been using to accelerate organic transformations. With the development
of environmental awareness, in order to obtain highly privileged scaffolds, scientists have directed their studies towards
the synthetic methodologies which minimize or preferably eliminate the formation of waste, avoid from toxic solvents and
reagents and use renewable starting materials as far as possible.
Methods:
In this connection, the organocatalytic reactions providing efficiency and selectivity for most of case have
become an endless topic in organic chemistry since several advantages from both practical and environmental standpoints.
Organocatalysts supplying transformation of reactants into products with the least possible waste production have been
serving to the concept of green chemistry.
Results and Conclusion:
Organocatalysts have been classified on the basis of their binding capacity to the substrate with
covalently or noncovalent interactions involving hydrogen bonding and electrostatic interaction. Diverse types of small
organic compounds including proline and its derivatives, phase-transfer catalysts, (thio)urease, phosphoric acids, sulfones,
N-oxides, guanidines, cinchona derivatives, aminoindanol and amino acids have been utilized as hydrogen bonding
organocatalysts in different chemical transformations.
Synthesis of cationic dibenzosemibullvalene-based phase-transfer catalysts by di-π-methane rearrangements of pyrrolinium-annelated dibenzobarrelene derivatives