Ruthenium(III) chloride (RuCl3)

Abstract

(A) A solvent-free Biginelli reaction utilizing RuCl3 was recently reported.20 The reaction was shown to be wide in scope covering aromatic, conjugated and aliphatic aldehydes to form either the pyrimidin-2(1H)-one or thione heterocycles. Acetonitrile was identified as an appropriate solvent if one was required. Yields were found to be very good for all reported reactions. (Chemical Equation Presented) (B) A reaction using RuCl3 to form a nitric oxide bound ruthenium dithiolate bridge complex was recently reported.21 The ability of ruthenium to reversibly complex nitric oxide has attracted attention for possible use in a number of biological applications. (Chemical Equation Presented) (C) Generation of RuO4 from RuCl3 is well documented for the formation of carboxylic acids and ketones from primary and secondary alcohols. Typical conditions employ NaIO4 as a stoichiometric oxidant in a biphasic solvent system (CCl4/MeCN/H2O). A recent paper by Ikunaka showcases a much more environmentally benign approach using trichloroisocyanuric acid as a stoichiometric oxidant, n-Bu4NBr as phase transfer catalyst and MeCN/H2O or EtOAc/H2O as solvent system. 22 Yields are comparable to traditional conditions using NaIO 4. (Chemical Equation Presented) (D) Deoxygenation of substituted aromatic N-oxides using stoichiometric RUCl3·xH2O has been reported.23 The methodology was also extended to incorporate azoxybenzenes and N-heteroarene oxides giving deoxygenated products in good yields. (Chemical Equation Presented) (E) Heterobimetallic Ru-Co nanoparticles, derived from ruthenium chloride and colloidal cobalt, were used in a Pauson-Khand-type reaction to access a number of bicyclic systems.24 The reaction also employed pyridylmethyl formate as a chemical alternative to carbon monoxide. High yields were observed for both intra- and intermolecular systems. (Chemical Equation Presented) (F) RuCl3 was found to effect the formation of arene heterocycles and carbocycles.25 The reaction requires AgOTf, presumably to activate the ruthenium in situ. Numerous catalytic systems, both Ru- and non-Ru-based, were explored with little success. (Chemical Equation Presented) (G) Michael addition of primary and secondary amines, thiols and carbamates to α,β-unsaturated esters, nitriles and ketones using catalytic RuCl3·PEG (polyethylene glycol) was recently reported.14 High yields were observed for all systems examined. The catalyst was recycled with little decrease in product yield. (Chemical Equation Presented). © Georg Thieme Verlag Stuttgart.