We found that cyclometalated cyclopentadienyl iridium(III) complexes are uniquely efficient catalysts in homogeneous hydrogenation of oximes to hydroxylamine products.As table iridium C,N-chelation is crucial, with alkoxy-substituted aryl ketimine ligands providing the best catalytic performance.S everal Ir-complexes were mapped by X-ray crystal analysis in order to collect steric parameters that might guide ar ational design of even more active catalysts.A broad range of oximes and oxime ethers were activated with stoichiometric amounts of methanesulfonic acid and reduced at room temperature,r emarkably without cleavage of the fragile N À Ob ond. The exquisite functional group compatibility of our hydrogenation system was further demonstrated by additive tests.E xperimental mechanistic investigations support an ionic hydrogenation platform, and suggest ar ole for the Brønsted acid beyond ap roton source.O ur studies providedeep understanding of this novel acidic hydrogenation and may facilitate its improvement and application to other challenging substrates.

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We found that cyclometalated cyclopentadienyl iridium(III) complexes are uniquely efficient catalysts in homogeneous hydrogenation of oximes to hydroxylamine products. A stable iridium C,N‐chelation is crucial, with alkoxy‐substituted aryl ketimine ligands providing the best catalytic performance. Several Ir‐complexes were mapped by X‐ray crystal analysis in order to collect steric parameters that might guide a rational design of even more active catalysts. A broad range of oximes and oxime ethers were activated with stoichiometric amounts of methanesulfonic acid and reduced at room temperature, remarkably without cleavage of the fragile N−O bond. The exquisite functional group compatibility of our hydrogenation system was further demonstrated by additive tests. Experimental mechanistic investigations support an ionic hydrogenation platform, and suggest a role for the Brønsted acid beyond a proton source. Our studies provide deep understanding of this novel acidic hydrogenation and may facilitate its improvement and application to other challenging substrates.

A General Synthesis of Tetrahydropyrazolo[3,4-d]thiazoles. -The short three step synthesis of the title compounds (VIII) allows the introduction of a wide range of substituents. The products are isolated as mixtures of two of four possible diastereomers. -(PELLETIER, S.; PINSON, B.; SMEJKAL, T.; LAMBERTH*, C.; Tetrahedron 69 (2013) 23, 4641-4651, http://dx.