Direct diazotization of indoles with 2-Methoxyethyl nitrite

Area of Science:

• Organic Chemistry
• Synthetic Chemistry
• Green Chemistry

Background:

• Diazo compounds are crucial synthetic intermediates for building complex carbon structures.
• Traditional C-H diazotization methods often involve hazardous reagents like azides or harsh acidic/basic conditions.
• There is a need for safer, more sustainable, and efficient diazotization protocols in organic synthesis.

Purpose of the Study:

• To develop a direct and sustainable method for the diazotization of indoles.
• To introduce 2-methoxyethyl nitrite (MOE-ONO) as a stable, reactive, and effective nitric oxide (NO) donor for C-H diazotization.
• To establish a greener protocol for synthesizing valuable diazo compounds from indoles.

Main Methods:

• Direct diazotization of 2-substituted indoles using 2-methoxyethyl nitrite (MOE-ONO).
• Employing TEMPO and catalytic Sc(OTf)3 as essential components in the reaction system.
• Utilizing MOE-ONO, synthesized from NO gas, oxygen, and 2-methoxyethanol, as a key reagent.

Main Results:

• MOE-ONO demonstrated superior reactivity and selectivity compared to traditional NO donors like tert-butyl nitrite or NaNO2/AcOH.
• The diazotization reaction proceeded efficiently in water, highlighting its green chemistry credentials.
• Synthesized 3-diazoindoles exhibited versatile reactivity, enabling Grignard reactions and rhodium-catalyzed cyclopropanations.

Conclusions:

• The developed MOE-ONO based diazotization protocol offers a sustainable and efficient alternative for indole functionalization.
• This method provides a practical route to highly functionalized indoles and indolines, important scaffolds in medicinal chemistry.
• The study effectively utilizes NO gas, contributing to cleaner chemical processes and waste reduction.