Alkyl derivatives hydrogenolysis

The case of butane is noteworthy since the selectivity at low conversions indicates that there is no selectivity in the overall hydrogenolysis step between n- and sec-butyl zirconium surface intermediates, while earUer studies had shown that the -alkyl zirconium complexes were more stable than sec-alkyl derivatives (Table 3 and Scheme 23) [94]. 

The potassium salt of 7-methyl-3-phenyl-2,4-dioxo-l,2,3,4-tetrahydropyrido[2,3- pyrimidine-5-carboxylate 153 was condensed with l-bromo-3-chloropropane or 1,4-dibromobutane in anhydrous DMF at room temperature to afford the A-l-alkyl derivatives 154 and 155, respectively <1994FA499>. The corresponding A-l-piperazinylalkyl derivatives of 153 were also prepared in more than 40% yield. Debenzylation of 6-benzyl-3-methylpyrido[4,3-,7 pyrimidine 156 by Pd/C-catalyzed hydrogenolysis in AcOH gave the analogue 157 <1994JHC1569>. 

Isoxazolidin-3-one 334, prepared by catalytic hydrogenolysis of 3-(benzyloxy)-4,5-dihydroisoxazole, reacted with l,4-dichloro-2-butyne in refluxing acetone in the presence of K2CO3 to give a 4 1 mixture of the regioisomeric N- and 0-alkyl derivatives (Scheme 82) <1999BMC1539>. 

Hydrogenation of diarylamines yields dialicyclic amines, but hydrogenolysis of the carbon-nitrogen bond also occurs. Dehydrogenation of DPA yields catbazole and alkyl derivatives of DPA give acridines. Dehydrogenation with sulfur gives phenothiazines (12). 

The early 80 s saw the beginning of the preparation and characterization of rare earth organo hydride compounds (Schumann and Genthe 1981, Evans et al. 1982b) by hydrogenolysis of Cp2Y, Er and Lu alkyl derivatives at atmospheric or high pressure. 

Unusual reducing properties can be obtained with borohydride derivatives formed in situ. A variety of reductions have been reported, including hydrogenolysis of carbonyls and alkylation of amines with sodium borohydride in carboxyHc acids such as acetic and trifluoroacetic (38), in which the acyloxyborohydride is the reducing agent. 

Mel, CH3CN morpholine or diethylamine, methanol, 76-95% yield. These conditions also cleave tlie 4 -pyridyl derivative. The Pet ester is stable to the acidic conditions required to remove the BOC and r-butyl ester groups, to the basic conditions required to remove the Fmoc and Fm groups, and to hydrogenolysis. It is not recommended for use in peptides that contain methionine or histidine since these are susceptible to alkylation with methyl iodide. 

Many of these catalysts are derived from metal complexes which, initially, do not contain metal hydride bonds, but can give rise to intermediate MH2 (al-kene) species. These species, after migratory insertion of the hydride to the coordinated alkene and subsequent hydrogenolysis of the metal alkyl species, yield the saturated alkane. At first glance there are two possibilities to reach MH2 (alkene) intermediates which are related to the order of entry of the two reaction partners in the coordination sphere of the metal (Scheme 1.2). 

Logarithms of relative rate constants for the hydrogenolysis of alkyl alkanoates were successfully correlated with a relationship derived from Equation 13 (lA) The results suggested a dependence on branching but due to collinearity were not conclusive. 

Since group 4 derived species are of particular interest as catalysts for olefin polymerization and epoxidation reactions, the thermal stability of surface metal-alkyl species, as weU as their reactivity towards water, alcohols and water, deserve some attention. On the other hand, mono(siloxy) metaUiydrocarbyl species can be converted into bis- or tris(siloxy)metal hydrides by reaction with hydrogen [16, 41, 46-48]. Such species are less susceptible to leaching and can be used as pre-catalysts for the hydrogenolysis of C-C bonds, alkane metathesis and, eventually, for epoxidation and other reactions. 

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