Dearomative indole (3 + 2) cycloaddition reactions.

Area of Science:

• Organic Chemistry
• Synthetic Chemistry
• Medicinal Chemistry

Background:

• Indoline scaffolds are prevalent in numerous natural products with significant biological activities.
• Developing efficient synthetic routes to complex fused indolines remains a key challenge in organic synthesis.

Purpose of the Study:

• To develop a novel diastereoselective (3 + 2) dearomative annulation reaction for synthesizing functionalized indoline derivatives.
• To demonstrate the utility of this methodology in the concise synthesis of natural product cores.
• To elucidate the reaction mechanism using computational studies.

Main Methods:

• Developed a diastereoselective (3 + 2) dearomative annulation of 3-substituted indoles with α-haloketones.
• Utilized Density Functional Theory (DFT) calculations (B3LYP-D3/6-311++G**/MeOH) to investigate reaction pathways.
• Applied the methodology to synthesize core structures of vincorine, isocorymine, and aspidophylline A.

Main Results:

• Achieved significant regiochemical control in the annulation reaction.
• Provided facile access to highly functionalized cyclopenta- and cyclohexa-fused indoline compounds.
• DFT studies supported the viability of both 2-hydroxyallyl cation and oxyallyl cation pathways, explaining regiochemical and stereochemical outcomes.

Conclusions:

• The developed annulation reaction is a powerful tool for constructing complex indoline frameworks.
• The methodology offers a concise route to valuable natural product structures.
• Computational analysis provides a detailed understanding of the reaction mechanism, including kinetic and thermodynamic preferences.