Dearomative (3 + 2) Cycloadditions of Unprotected Indoles

Area of Science:

• Organic Chemistry
• Synthetic Methodology
• Cycloaddition Reactions

Background:

• Indole derivatives are crucial in medicinal chemistry and materials science.
• Developing selective and efficient methods for functionalizing indoles is an ongoing challenge.
• Dearomatized cyclopentannulated structures are valuable synthetic targets.

Purpose of the Study:

• To develop a novel (3 + 2) cycloaddition reaction for indole functionalization.
• To achieve high regio-, chemo-, and diastereoselectivity in the synthesis of cyclopentannulated indoles.
• To demonstrate the utility of the reaction in late-stage derivatization of complex indole substrates.

Main Methods:

• Employing a (3 + 2) cycloaddition between various indoles and a dithioallyl cation.
• Utilizing a strong Brønsted acid catalyst in excess to control reactivity.
• Investigating the reaction's tolerance to sensitive functional groups.

Main Results:

• Synthesis of dearomatized cyclopentannulated adducts from indoles.
• Complete control over regioselectivity and excellent chemo- and diastereoselectivity were achieved.
• The reaction successfully tolerated sensitive functionalities like amines and hydroxyl groups.
• Demonstrated late-stage derivatization of unprotected, highly functionalized indoles.

Conclusions:

• The developed (3 + 2) cycloaddition provides a powerful and selective route to valuable indole adducts.
• The use of excess strong Brønsted acid is key to preventing side reactions and ensuring high yields.
• This methodology offers a versatile tool for the synthesis of complex indole-containing molecules.