Hydride copper

The presence of transition metal ions has a catalytic effect on reduction of halides and tosylates by LiAlH4.166 Various copper hydride reducing agents are effective for removal of halide and tosylate groups.167 The primary synthetic value of these reductions is for the removal of a hydroxy function after conversion to a halide or tosylate. 

Scheme 5.7 illustrates these and other applications of the hydride donors. Entries 1 and 2 are examples of reduction of alkyl halides, whereas Entry 3 shows removal of an aromatic halogen. Entries 4 to 6 are sulfonate displacements, with the last example using a copper hydride reagent. Entry 7 is an epoxide ring opening. Entries 8 and 9 illustrate the difference in ease of reduction of alkynes with and without hydroxy participation. 

Copper hydride species, notably Stryker s reagent [Ph3PCuH]6, are capable of promoting the conjugate reduction of a,( >-unsalurated carbonyl compounds [42], Taking advantage of this trustworthy method, Chiu et al. demonstrated in 1998 an intramolecular reductive aldol reaction in the synthesis of novel terpenoid pseudolaric acids isolated from Chinese folk medicine (Scheme 28) [43]. Two equivalents of [Ph3PCuH]6 enabled cycli-zation of keto-enone 104 to provide the bicyclic diastereomers 105 (66%) and 106 (16%). The reaction also was applied to the transformation of 107... 

Potassium, sodium and copper hydrides all ignite in chlorine at ambient temperatures. 

Mellor, 1940, Vol. 2, 12, 483 1956, Vol. 2, Suppl. 1, 56 1941, Vol. 3, 73 Copper hydride, potassium hydride and sodium hydride all ignite on contact with fluorine at ambient temperature. 

INVERSE ELECTRON-DEMAND DIELS-ALDER CYCLOADDITION OF A KETENE DITHIOACETAL. COPPER HYDRIDE-PROMOTED REDUCTION OF A CONJUGATED ENONE. 9-DITHIOLANOBICYCLO[3.2.2]NON-6-EN-2-ONE FROM TROPONE... 

The 3-trifluoromethylsulfonyloxy-3A-cephem 84 is converted to the norcephalosporin 85 at 130 °C and 3-nor-2A-cephalosporin 86 at 0 °C by the action of copper hydride, formed from tributyltin hydride and copper chloride in A-methylpyrrolidone <99JCS(P1)3463>. 

More Recent Developments Stoichiometric Copper Hydride Reagents... 

Among its salient features, this copper hydride (written for simplicity from now on as the monomer (Ph3 P)CuH) can be prepared in multi-gram quantities from four precursor compounds (CuCl, NaO-t-Bu, PPh3, and H2) that are not only readily available but also very inexpensive (Eq. 5.5) [15]. It is also noteworthy that the byproducts of formation (NaCl and t-BuOH) are especially environmentally friendly . 

The successes described above notwithstanding, synthetic chemistry in the 1990s was in large measure characterized by catalysis , which encouraged development of organocopper processes that were in line with the times. The cost associated with the metal was far from the driving force that was more (and continues to be) a question of transition metal waste. In other words, proper disposal of copper salt by-products is costly, and so precludes industrial applications based on stoichiometric copper hydrides. 

A fascinating study on the surface science of copper hydride on Si02, as well as on AI2O3, ceria (cerium oxide), and ZnO, has appeared [50]. Pure, yet thermally unstable, CuH can be precipitated as a red-brown solid from aqueous cupric sulfate and hypophosphorous acid in the presence of H2SO4, and has been characterized by powder X-ray diffraction (PXRD) (Eq. 5.25). Transmission electron microscopy (TEM) data suggest that it is most stable when deposited on acidic Si02. 

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