A facile synthesis of pyrazole, isoxazole and pyrimidine ortho-dicarboxylic acid derivatives via β-enaminoketoesters

Ethyl 5-(4-amino-phen-yl)isoxazole-3-carboxyl-ate

The asymmetric unit of the title compound, C₁₂H₁₂N₂O₃, contains two mol­ecules in which the benzene and isoxazole rings are almost coplanar, the dihedral angles between their mean planes being 1.76 (9) and 5.85 (8)°. The two mol­ecules inter­act with each other via N—H⋯N and N—H⋯O hydrogen bonds, which link the mol­ecules into layers parallel to the ac plane. The layers stack in a parallel mode with an inter­layer distance of 3.36 (7) Å.

Synthesis of N-methoxy-N-methyl-beta-enaminoketoesters: new synthetic precursors for the regioselective synthesis of heterocyclic compounds

[Structure: see text] Weinreb amides react with the lithium or sodium acetylide of ethyl propynoate in a hitherto unexplored acyl substitution-conjugate addition sequence to furnish (E)-N-methoxy-N-methyl-beta-enaminoketoesters. This approach provides a diverse entry to densely functionalized heterocyclic compounds, including pyrazoles through regioselective cyclocondensations with hydrazines in a microwave-assisted reaction.

A “Catch and Release” Strategy for the Parallel Synthesis of 2,4,5-Trisubstituted Pyrimidines

A resin capture and release strategy for making a combinatorial array of 2,4,5-trisubstituted pyrimidines is demonstrated by capturing beta-ketoesters and beta-ketoamides on a solid-supported piperazine. Through a cyclocondensation reaction, the solid-supported enaminone is reacted with several guanidines under heating or microwave irradiation affording the corresponding pyrimidines in good yield and chemical purity directly on solution. After this final step, the support can be effectively recycled.