Synthetic Routes to Pyrazole-3(5)-carboxylates

Ethyl 1-phenyl-1,4-dihydroindeno[1,2-c]pyrazole-3-carboxylate

The non-H atoms of the title molecule, C19H16N2O2, are almost coplanar (r.m.s. deviation = 0.019 Å), apart from the phenyl group, which is disordered with two components of almost equal occupancy: the dihedral angle between them is 78.9 (3)°. In the crystal, weak C—H...N hydrogen bonds link the molecules into [001] chains and aromatic π–π stacking interactions [shortest centroid–centroid separation = 3.747 (2) Å] form columns parallel to the c-axis direction.

Laboratory-Scale Membrane Reactor for the Generation of Anhydrous Diazomethane

A configurationally simple and robust semibatch apparatus for the in situ on-demand generation of anhydrous solutions of diazomethane (CH2N2) avoiding distillation methods is presented. Diazomethane is produced by base-mediated decomposition of commercially available Diazald within a semipermeable Teflon AF-2400 tubing and subsequently selectively separated from the tubing into a solvent- and substrate-filled flask (tube-in-flask reactor). Reactions with CH2N2 can therefore be performed directly in the flask without dangerous and labor-intensive purification operations or exposure of the operator to CH2N2. The reactor has been employed for the methylation of carboxylic acids, the synthesis of α-chloro ketones and pyrazoles, and palladium-catalyzed cyclopropanation reactions on laboratory scale. The implementation of in-line FTIR technology allowed monitoring of the CH2N2 generation and its consumption. In addition, larger scales (1.8 g diazomethane per hour) could be obtained via parallelization (numbering up) by simply wrapping several membrane tubings into the flask.

Brönsted acid-mediated annulations of 1-cyanocyclopropane-1-carboxylates with arylhydrazines: efficient strategy for the synthesis of 1,3,5-trisubstituted pyrazoles

A diversity-oriented synthesis of 1H-pyrazole derivatives via Brönsted acid-promoted annulations of 1-cyanocyclopropane-1-carboxylates with arylhydrazines has been developed.