C2-Selective Palladium-Catalyzed C-S Cross-Coupling of 2,4-Dihalopyrimidines

Area of Science:

• Organic Chemistry
• Catalysis
• Medicinal Chemistry

Background:

• 2,4-Dihalopyrimidines typically undergo substitution reactions at the C4 position under most conditions.
• Palladium-catalyzed cross-coupling reactions involving pyrimidines predominantly favor C4 selectivity, limiting synthetic applications.

Purpose of the Study:

• To develop a novel catalytic system for regioselective C2-functionalization of 2,4-dichloropyrimidine.
• To investigate the influence of palladium(II) precatalysts with N-heterocyclic carbene ligands on cross-coupling selectivity.
• To explore the utility of this C2-selective reaction in diversity-oriented synthesis, including antiviral drug derivatives.

Main Methods:

• Utilized palladium(II) precatalysts supported by bulky N-heterocyclic carbene ligands.
• Performed cross-coupling reactions of 2,4-dichloropyrimidine with various thiols and thiophenols.
• Analyzed regioselectivity, sensitivity to precatalyst structure, and competing nucleophilic aromatic substitution pathways.

Main Results:

• Achieved unprecedented C2-selective cross-coupling of 2,4-dichloropyrimidine with thiols, contrasting with the typical C4 selectivity.
• Demonstrated high C2-selectivity with primary thiols and thiophenols, and applicability to substituted dichloropyrimidines.
• Observed high sensitivity of selectivity to the precatalyst structure, attributed to competing C4-selective nucleophilic aromatic substitution.

Conclusions:

• Developed a unique catalytic system enabling C2-selective functionalization of 2,4-dichloropyrimidine via palladium catalysis.
• The findings challenge conventional understanding of pyrimidine cross-coupling regioselectivity and may involve non-traditional C2-Cl bond cleavage mechanisms.
• This regioselective transformation offers a valuable tool for diversity-oriented synthesis, particularly for biologically relevant molecules like antiviral agents.