Metal-induced reaction

Competition between metal ion-induced and radical-induced decompositions of alkyl hydroperoxides is affected by several factors. First, the competition is influenced by the relative concentrations of the metal complex and the hydroperoxide. At high concentrations of the hydroperoxide relative to the metal complex, alkoxy radicals will compete effectively with the metal complex for the hydroperoxide. Competition is also influenced by the nature of the solvent (see above). Contribution from the metal-induced reaction is expected to predominate at low hydroperoxide concentrations and in reactive solvents. The contribution from the metal-induced decomposition to the overall reaction is readily determined by carrying out the reaction in the presence of free radical inhibitors, such as phenols, that trap the alkoxy radicals and, hence, prevent radical-induced decomposition.129,1303 Thus, Kamiya etal.129 showed that the initial rate of the cobalt-catalyzed decomposition of tetralin hydroperoxide, when corrected for the contribution from radical-induced decomposition by the... 

The fundamental chemistry of donor-acceptor-substituted cyclopropanes is now well understood. This solid platform should allow many applications of known processes and exploration of new reaction types. A future challenge will be asymmetric syntheses which should be achievable, for instance, using Lewis acids containing enantiomerically pure ligands. Even more attractive might be cyclopropane formation under the influence of a suitable optically active catalyst. This intriguing approach could lead to enantioselective syntheses of many compounds in a most economical way. Finally it can be expected in the near future that transition metal induced reactions will also play an important role in this area of small ring chemistry. 

Product analysis shows that the thermal and metal induced reactions follow similar courses. The former reaction may proceed by opening of one ring to produce a formal vinyl carbene, followed by ring expansion the latter may be rationalised in terms of electrophilic attack by silver ion at one of the cyclopropenes to produce a carbenium ion (355) — that is a silver-coordinated equivalent of the carbene — followed by ring expansion of the second cyclopropene. 

Reaction of 2H-Azirines with Electrophiles and Metal-Induced Reactions... 

Asymmetric synthesis has become the most relevant route to enantiomerically pure compounds, and transition-metal-induced reactions are increasingly important in the array of methods for the enantioselecdve construction of new asymmetric centers. Catalytic processes, in which chiral information is transferred from a small fraction of a chiral... 

Diazoalkanes 1 form a versatile class of functionalized organic compounds [1]. Their undisputed significance in organic synthesis is manifested in a number of organometallic and other metal-induced reactions [2], some of which have entered catalytic applications. Cyclopropanation is one of them (cf. Section 3.1.7) but intramolecular carbon-hydrogen insertion appears of much potential in synthesis, too. This type of reaction relates to the easily available, normally nonexplosive a-diazocarbonyl compounds (a-diazoketones. Structure 2). 

Cyclopropenes may undergo [2 + 2] cycloaddition to themselves, to form dimers, or to other alkenes the reactions may be brought about by photolysis, metal catalysis, Lewis acid catalysis, or simply by heat. Due to the difficulties that can be encountered in completely purifying some cyclopropenes, it is possible that some thermal reactions are actually initiated by small quantities of impurity. The following sections include those reactions occurring under thermal and Lewis acid catalysis, Those brought about by photolysis are covered in Section Ll.6.2.3.1,1. metal-induced reactions are dealt with in Section 1.1.6.3.3. 

Oxidation of hydrocarbons has been known for many years to involve the formation of key intermediate hydroperoxides and dialkylperoxides ( peroxides in general) from the reaction of oxygen and hydrocarbons via free radical intermediates. At low temperatures, the peroxides formed slowly accumulate and eventually decompose either thermally or by metal-induced reactions or by ionic routes. At high temperatures, formation and thermal decomposition of the peroxides occurs rapidly. Thermal decomposition leads to the production of additional free radicals (the propagation step of the reaction) and the formation of oxygen-containing products (e.g., acids, alcohols, ketones, polar compounds, and polymeric materials) that can ultimately bring about lubricant failure. 

A report by the Corriu group, however, shows that this is not necessarily the case (equation 49) . When difluorosilane was treated with lithium metal in the presence of dimethylbutadiene, the silacyclopentene was obtained in good yield but no silylene was intercepted if EtsSiH was present as the trapping agent. The product silacyclopentene could result either from reaction of the diene with a silylenoid, or from reaction of the diene with lithium and trapping of the lithium compound by the difluorosilane. In earlier studies of the alkali metal induced reactions of dihalosilanes with 1,3-dienes, it was found that the diene, rather than the dihalosilane, reacts initially with the metal. ... 

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