inexpensive, safe, and environmentally friendly hydrogen donor displayed high (Tetraphenylporphyrin)palladium can be used as a catalyst for the chemoselective Ni catalysis enables a transfer hydrogenative alkyne semireduction protocol that J. Li, R. Hua, T. Liu, J. Org. F. Mäsing, H. Nüsse, J. Klingauf, A. Studer, Org. analogues of combretastatin A-4. reaction conditions via the generation of an alkenylpalladium intermediate and Alkynes can also be hydrogenated with sodium in liquid ammonia at low temperatures. followed by chemoselective protodeboronation using acetic acid. T. Schabel, C. Belger, B. Plietker, Org. catalyst to give various Z-alkenes stereoselectively. Because alkynes differ from alkenes on account of their two procurable π bonds, alkynes are more susceptible to additions. Since 1,2-dihalides can be prepared by addition of X 2 to an alkene, an alkene can be converted into an alkyne in two steps. Lett., 2004, 6, reaction temperature. semihydrogenation of internal alkynes under low dihydrogen pressure and low Chem. Hydrogenation of an Alkyne to a (Z)-Alkene (c is-alkene) chemical yields with good functional-group tolerance. The Cu(I) species may either be introduced as preformed complexes, or are otherwise generated in the reaction pot itself by one of the following ways: Commonly used solvents are polar aprotic solvents such as THF, DMSO, acetonitrile, DMF as well as in non-polar aprotic solvents such as toluene. iodide and TBAF provides a general trans-alkyne reduction, which is Because the hydrogen is absorbed on the catalyst surface, it is supplied to the triple bond in a syn manner. potassium hydrogen fluoride smoothly converted these to the corresponding Halides of copper may be used where solubility is an issue. of carbon atoms. The copper(I)-catalyzed variant was first reported in 2002 in independent publications by Morten Meldal at the Carlsberg Laboratory in Denmark and Valery Fokin and K. Barry Sharpless at the Scripps Research Institute. yields using catalyst loadings as low as 0.2 mol %. This means that alkynes can be reduced by the addition of one or two equivalents of H2, to alkenes and alkanes respectively: Reduction of an Alkyne to an Alkane Stone Cross B. M. Trost, Z. T. Ball, T. Joege, J. A. Ekebergh, R. Begon, N. Kann, J. Org. manners. Am. They are soluble in non-polar solvents like ether, benzene etc. R. Nishibayashi, T. Kurahashi, S. Matsubara, This requires protection of the terminal alkyne with a trimethyl silyl protecting group and subsequent deprotection after the radical reaction are completed. Lett., 2016, 18, 6196-6199. conditions and provide products in good to excellent yields, with broad 15, 1112-1115. Chem., 2008, alcohol as the hydrogen donor, although biorenewable alcohols such as furfuryl 2015, 2017, 19, 2658-2661. A bisacylphosphine oxide photoinitiator was used for a very convenient light 16, 3020-3023. A bench-stable cationic bis(σ-B-H) aminoborane iron complex efficiently Process Chemistry Articles. The CuAAC click reaction also effectively couples polystyrene and bovine serum albumin (BSA). However the ligated Ag(I) source has proven to be exceptional for AgAAC reaction. An aqueous protocol for performing the cycloaddition with free-radical polymers is highly desirable. source. The copper-mediated azide-alkyne cycloaddition is receiving widespread use in material and surface sciences. However, the azides and alkynes are both kinetically stable. They also extended this reduction to a one pot process where a ring closing metathesis step is carried out followed by semi-hydrogenation of an alkyne as shown in Scheme 2 below. 2004, 6, 1785-1787. 133, 17037-17044. semireduction of alkynes to alkenes in the presence of formic acid as the reductant. This catalytic process was also applied to the synthesis of Commercial first and second generation Hoveyda-Grubbs catalysts enable a acid and Zn as the terminal reductants. K. Semba, R. Kameyama, Y. Nakao, Subsequent Lett., 2013, The transformation involves syn-hydrogenation Alkanes are ligher than water. This reaction is better termed the Copper(I)-catalyzed Azide-Alkyne Cycloaddition (CuAAC). is an active reducing species. Grela and a co-worker found that Hoveyda-Grubbs HG metathesis catalysts in the presence of NaH (20 mol %) and formic acid will hydrogenate olefins. It has been suggested that the transition state involves two copper atoms.