Everything about Cascade Reaction totally explained
A
cascade reaction or
tandem reaction or
domino reaction is a consecutive series of
intramolecular organic reactions which often proceed via highly
reactive intermediates. It allows the
organic synthesis of complex multinuclear molecules from a single
acyclic precursor. The substrate contains many
functional groups that take part in chemical transformations one at the time. Often a functional group is generated
in situ from the previous chemical transformation. The definition includes the prerequisite
intramolecular in order to distinguish this reaction type from a
multi-component reaction. In this sense it differs from the definition of a
biochemical cascade. The main advantages of a cascade reaction in organic synthesis are that the reaction is often fast due to its intramolecular nature, the reaction is also clean, displays high
atom economy and doesn't involve workup and isolation of many intermediates.
A cascade reaction is sometimes called a
living reaction because it shares some characteristics with a
living polymerization. In cascade reactions one can identify an initiation site, a relay moiety and a termination moiety. Examples of cascade reactions are numerous (for example the
Aldol-Tishchenko reaction) and especially so in
alkyne chemistry (the
Banert cascade to name just one) or
polyolefin polycycloisomerizations. Other alkyne
coupling reactions are classified based on common features such as type of compound synthesised, for instance the
spiro mode cascade :
or the linear-
fused mode cascade ,through application of the intramolecular
Heck reaction:
or the zipper mode cascade .
Other cascade reactions are included in
Diels-Alder reactions,
oxirane ring-opening reactions , and
Pauson–Khand reactions .
An example of an
oxirane cascade reaction is given by the synthesis of certain
polyether ladder polymers :
This type of ladder compounds are found in marine lifeforms such as
red tide. The tri-
epoxide is prepared from a triene through
asymmetric Shi epoxidation and
oxone as primary
oxidizing agent. The hydroxyl group in the tri-epoxide is activated as a
nucleophile by the presence of the base
caesium carbonate The bulky
trimethylsilyl groups make such that the polyether is formed with the correct
stereochemistry and they're removed
in situ by
caesium fluoride.
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