Chemo- and Regioselective Catalytic Reduction of N‑Heterocycles by Silane
journal contributionposted on 26.08.2013, 00:00 by Sun-Hwa Lee, Dmitry V. Gutsulyak, Georgii I. Nikonov
The ruthenium complex [Cp(iPr3P)Ru(NCCH3)2]+ (1) catalyzes the regioselective hydrosilylation of pyridines to 1,4-dihydropyridines. Substitution in the 3- and 5-positions is tolerated, whereas pyridines with substituents in the 2-, 4-, and 6-positions are not reduced. Reduction of functionalized pyridines having keto and ester substituents results in a mixture of products. N-Silyl-1,4-dihydropyridine reacts with ketones and aldehydes to give products of N–Si addition across the CO bond. Hydrosilylation of pyridine in acetone results quantitatively in the addition product PhMe2SiO–CMe2–NC5H6, which decomposes in hexane to give the parent dihydropyridine HNC5H6. The phenanthroline complex [Cp(phen)Ru(NCCH3)2]+ (10) catalyzes regioselective 1,4-reduction of phenanthroline by a 3–4-fold excess of silane/water or silane/alcohol mixtures. The Cp* analogue [Cp*(phen)Ru(NCCH3)2]+ (9) catalyzes 1,4-regioselective monohydrosilylation of phenanthroline, quinoline, acridine, and 1,3,5-triazine and the 1,2-reduction of isoquinoline. In contrast, 2-substituted phenanthroline, pyrazine, 2-ethylpyridine, 2,6-lutidine, 2,4-lutidine, and pyrimidine are not reduced under these conditions by either of the catalysts studied.