Temperature-modulated selective C(sp³)-H or C(sp²)-H arylation through palladium catalysis

Area of Science:

• Organic Chemistry
• Catalysis
• Medicinal Chemistry

Background:

• Transition metal-catalyzed C-H bond functionalization is vital in organic and medicinal chemistry.
• Selective activation of C(sp³)-H and C(sp²) bonds presents significant synthetic challenges.
• Developing new directing groups is crucial for advancing C-H activation methodologies.

Purpose of the Study:

• To demonstrate the first temperature-dependent selective C-H functionalization of unactivated C(sp³)-H or C(sp²) bonds.
• To utilize a novel 7-pyridyl-pyrazolo[1,5-a]pyrimidine directing group for remote C-H activation.
• To explore palladium catalysis for achieving high selectivity in C-H functionalization.

Main Methods:

• Employing palladium catalysis with 7-pyridyl-pyrazolo[1,5-a]pyrimidine as a directing group.
• Investigating temperature-dependent C-H activation at 120 °C (C(sp³)-H) and 140 °C (C(sp²)-H).
• Utilizing catalytic amounts of Pd(OAc)₂ and AcOH.
• Conducting mechanistic studies involving palladacycle intermediates and tetramer formation.

Main Results:

• Achieved selective C(sp³)-H arylation at 120 °C via a [6,5]-fused palladacycle.
• Observed selective C(sp²)-H arylation at 140 °C through a 16-membered tetramer intermediate.
• Identified a common 6-membered palladacycle intermediate for both activation pathways.
• Demonstrated temperature-induced conversion of the [6,5]-fused palladacycle to the tetramer.

Conclusions:

• The developed palladium-catalyzed system enables unprecedented temperature-dependent selective C-H functionalization.
• The 7-pyridyl-pyrazolo[1,5-a]pyrimidine directing group facilitates remote C-H activation.
• This work provides a new strategy for controlling C-H activation selectivity through temperature modulation.