Palladium cycloalkanes

Trost and coworkers137 have reported the polymer-supported palladium catalyzed cyclization of 1, l-bis(phenylsulfonyl)epoxyalkene 235 which gives cycloalkanes 236 and 237 in a 2 1 ratio (equation 143). This method has proven useful for the synthesis of macrocyclic compounds under neutral conditions without using high dilution technique. Temperature and concentrations are critical. The best results are achieved if a reaction mixture of 0.1-0.5 m is added to a preheated (at 65 °C) suspension of the catalyst. 

Stannaboration of diynes and enyne provide cycloalkanes incorporating both stannyl and boryl groups, which are otherwise difficult to synthesize. Palladium-catalyzed reactions of 1,4-, 1,5-, and 1,6-diynes with 9 give the corresponding cyclization products in good yields (Equation (99)).247 The reaction is so efficient that even a strained four-membered ring is readily formed. 

Reduction of cycloalkane-condensed 2-phenyl-5,6-dihydro-4//-l,3-benzoxazines 144 with lithium aluminium hydride (LAH) afforded A -benzyl-substituted 2-(aminomethyl)cycloalkanols 145 in a reductive ring opening via the ring-chain tautomeric tetrahydro-l,3-oxazine intermediates. Catalytic reduction of 1,3-oxazines 144 under mild conditions in the presence of palladium-on-carbon catalyst similarly resulted in formation of the A -benzyl-1,3-amino alcohols 145. When the catalytic reduction was performed at elevated temperature at hydrogen pressure of 7.1 MPa, the N-unsubstituted 2-(aminomethyl)cycloalkanols 146 were formed in good yields (Scheme 22) <1998SC2303>. 

Nickel has been reported to show behaviour similar to platinum [236], Further, in the reactions of cycloalkenes with deuterium, the product cycloalkanes are much more extensively exchanged over palladium than over nickel or platinum [236]. Such behaviour is not unexpected by comparison with the results obtained in the hydrogenation of linear alkenes (Sect. 3, p. 25). 

Iodine-Mercury(II) oxide, 149 a-METHYLENE ALDEHYDES AND KETONES 1,4-Diazabicyclo[2.2.2]octane, 92 Dimethyl sulfoxide, 124 Formaldehyde, 136 Methoxyallene, 177 Methylene cycloalkanes By cyclization reactions Diacetatobis(triphenylphos-phine)palladium(II), 91 l-Hydroxy-3-trimethylsilylmethyl-3-butene, 147... 

Palladium-gold on alumina catalysts are examples of bifunctional catalysts (3,4), in which the alumina carrier itself possesses acidic sites that are involved in the reactions. This property of the system impedes a detailed understanding of the effect of the gold in suppressing the formation of C,-C6 alkanes. However, when alkanes or cycloalkanes are contacted with simpler metal catalysts, specifically, metals which are either unsupported or supported on a relatively nonacidic carrier such as silica, a similar marked suppression in the formation of products of lower carbon number than the reactants is observed when a Group IB metallic element is incorporated with a Group VIII metal. Examples are given in our 1971 patent (5), for which the... 

The isotopic exchange reaction between deuterium and (+)3-methyl-hexane on nickel and palladium catalysts at temperatures above 100° leads to racemization of the optically active hydrocarbon. In exchange between deuterium and cycloalkanes at temperatures between —50° and about 75°, a discontinuity separates the concentrations of C H D and. In cyclopentane at about 50°, for example, exchange... 

Cycloalkanes and cycloalkanes containing one or more six-memberea rings can usually be dehydrogenated to the corresponding benzoid derivatives by heating to a high temperature with a platinum or palladium catalyst. 

To appreciate how important alkyl reversal is in the reactions being considered, the reactions of monosubstituted Ce cycles with deuterium are informative the results obtained with carbon-supported metals after 25% addition are given in Table 7.7 Remembering that deuterium numbers M of the cycloalkane greater than two mean more hydrogen exchange than cycloalkene exchange, and vice versa, the results are broadly in line with the characteristics of the three metals as exposed in the earlier sections. A certain amount of alkyl reversal must occur in all cases, but alkene desorption is only important with palladium. With Pt/C... 

Kariya et al. performed dehydrogenation of methylcyclohexane and other cycloalkanes over platinum, palladium and rhodium monometallic and platinum/palladium, platinum/rhodium, platinum/molybdenum, platinum/tungsten, platinum/rhenium platinum/osmium and platinum/iridium catalysts supported on both petroleum coke active carbon and on alumina between 375 and 400 °C [279]. The platinum catalyst supported by petroleum active carbon showed the highest activity. While platinum was the most active monometallic catalyst, its activity could be increased by addition of molybdenum, tungsten and rhenium. 

A similar situation exists in the hydroxymercuration and thallium(m) oxidation of cycloalkenes and cycloalkanes, the rate laws showing strict second-order behaviour for both metal ions. In the thallium(ni) reactions two products have been observed, a 1,2-diol and a ketone or aldehyde. Two-electron coupling with trifluoroacetate has been shown to promote oxidative phenol coupling. The mechanism of oxidation of olefins by palladium(n) has been investigated. In the presence of PdClg in aqueous media, the data conform to the rate expression... 

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