Access to Highly Strained Tricyclic Ketals Derived from Coumarins

Area of Science:

• Organic Chemistry
• Synthetic Chemistry
• Heterocyclic Chemistry

Background:

• Coumarin derivatives are versatile scaffolds in medicinal chemistry and materials science.
• The synthesis of strained fused ring systems presents unique synthetic challenges.
• Understanding reaction mechanisms is crucial for developing novel synthetic methodologies.

Purpose of the Study:

• To report the synthesis of novel, highly strained fused dihydrobenzopyran cyclopropyl lactones.
• To investigate the influence of substituents on the coumarin ring on lactone formation.
• To elucidate the mechanism of the observed intramolecular rearrangement.

Main Methods:

• Synthesis of substituted coumarin carboxylates.
• Cyclization reactions to form fused lactone structures.
• Mechanistic studies involving proposed intermediates and rearrangements.

Main Results:

• Successful synthesis of fused dihydrobenzopyran cyclopropyl lactones from coumarin carboxylates.
• Demonstrated tolerance for various 6- and 8-substituents on the coumarin core.
• Identified resistance to tricyclic lactone formation at 5- and 7-positions, except for 7-methyl substitution.
• Observed formation of tricyclic ketals from benzamide-containing coumarins.
• Proposed a mechanism involving intramolecular rearrangement of trans cyclopropyl methyl ketones.

Conclusions:

• A novel synthetic route to highly strained fused lactones has been established.
• Substituent effects on the coumarin ring dictate the feasibility of tricyclic lactone formation.
• The proposed mechanism provides valuable insights into the formation of these complex heterocyclic systems.