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Do you know what the Thiol-ene reaction is? What amazing applications can this magical chemical reaction bring?
In organosulfur chemistry, the thiol-ene reaction is an organic reaction that combines thiols (R−SH) and olefins (R2C=CR2) to form thioethers (R−S−R'). The reaction was first reported in 1905, but gained prominence in the late 1990s and early 2000s, becoming famous for its feasibility and wide range of applications.
The thiol-ene reaction is considered a "terrific" chemical reaction because of its high yield, stereoselectivity, high reaction rate and thermodynamic driving force.
This reaction realizes the trans-Markovnikov addition of thiol compounds to olefins. Given its stereoselectivity, high reaction rate, and high yield, this synthetically valuable reaction may form the basis for future applications in materials and biomedical sciences.
Reaction Mechanism
Free Radical Addition
There are two main mechanisms of thiol-ene addition: free radical addition and catalytic Michael addition. The free radical addition can be initiated by light, heat or a free radical initiator and generates a sulfonyl radical. The free radical will then propagate with the olefin functional group in a trans-Markovnikov manner to form a carbon radical.
This free radical reaction is advantageous for chemical synthesis because the step growth and chain growth processes can effectively form a uniform polymer network.
Michael Bonus
Thiol-ene reactions can also proceed via the Michael addition pathway, which is catalyzed by radicals or nucleophiles to form similar trans-Markovnikov addition products.
Dynamics
Although click chemistry is known for its high efficiency and fast reaction rate, the overall reaction rate still depends on the functionality of the olefin. Studies have shown that the reactivity and structure of olefins influences whether reactions follow a step-growth or chain-growth path.Synthetically Useful Thiol-ene Reactions
Initiation of cascade cyclization
Thiol-ene (and similar thiyl-yne) reactions are widely used to generate reaction intermediates of unsaturated substrates that can initiate cyclization reactions.
Intramolecular Thiol-ene reaction
These reactions provide a method for creating sulfur-containing heterocycles and can generate four- to eight-carbon rings as well as macrocycles.
Chair-twist transformation of olefins
Due to the reversibility of Thiol-ene radical addition, the reaction can promote cis-trans isomerization and achieve different stereochemistry through the rotation of carbon radical intermediates.
Potential ApplicationsDendrimer Synthesis
Dendrimers are valued for their potential in medicine, biomaterials, and nanoengineering. Thiol-ene addition has utility in the branched synthesis of dendrimers.
Polymer Synthesis
Multifunctional thiols react with multifunctional olefins to rapidly form cross-linked polymer networks in a quantitative manner under atmospheric conditions.
Surface pattern design
Surface functionalization of thiol-ene has been extensively studied in materials science and biotechnology. The technique enables precise spatial control of functional molecules and can selectively expose the surface based on the composition of the gravure and aqueous phases.
Protein patterning in electron beam resists
Thiol-ene can also be used as an electron beam resist and fabricated into nanostructures to allow direct protein functionalization.
The uniqueness and potential applications of the thiol-ene reaction make it a research area full of opportunities. But how will this technology affect our lives and the field of science in the future?
