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Azanorbornadienes as Thiol-Reactive Cleavable Linkers.
Organic Letters
|August 19, 2020
Summary
Azanorbornadienes (ZNDs) react with thiols and then cleave to release pyrroles. Sulfonylated ZNDs are more stable to cleavage than acylated versions, offering tunable reactivity for chemical synthesis.
Area of Science:
- Organic Chemistry
- Synthetic Chemistry
Background:
- Azanorbornadienes (ZNDs) are heterocyclic compounds derived from pyrroles.
- Their reactivity in Michael additions and retro-Diels-Alder (rDA) reactions is of interest for synthetic applications.
- Compared to oxanorbornadienes, ZNDs offer unique structural modifications.
Purpose of the Study:
- To investigate the reactivity of Azanorbornadienes (ZNDs) in Michael reactions with thiols.
- To explore the influence of substituents on the pyrrole nitrogen on ZND stability and cleavage.
- To compare the reactivity and stability of different ZND derivatives.
Main Methods:
- Synthesis of Azanorbornadienes (ZNDs) from pyrroles.
- Reaction of ZNDs with thiols to study Michael addition.
- Analysis of retro-Diels-Alder (rDA) cleavage products and kinetics.
- Comparison of acylated, sulfonylated, and tert-butoxycarbonyl protected ZNDs.
Main Results:
- ZNDs undergo Michael addition with thiols, followed by rDA cleavage to yield pyrroles and thiomaleates.
- Sulfonylated ZNDs exhibit enhanced stability against rDA cleavage compared to acylated analogues.
- Tert-butoxycarbonyl protected ZNDs show reduced reactivity towards thiols, slowing the overall reaction sequence.
Conclusions:
- Azanorbornadienes provide a versatile platform for chemical transformations.
- Nitrogen substitution significantly impacts ZND stability and reactivity in thiol additions and rDA cleavage.
- The findings enable the rational design of ZNDs for controlled release applications or further synthetic elaborations.
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