Insertion into hydrogen-carbon bond

Like carbene insertions into carbon-hydrogen bonds, metal nitrene insertions occur in both intermolecular and intramolecular reactions.For intermole-cular reactions, a manganese(III) meio-tetrakis(pentafluorophenyl)porphyrm complex gives high product yields and turnovers up to 2600 amidations could be effected directly with amides using PhI(OAc)2 (Eq. 51). The most exciting development in intramolecular C—H reactions thus far has been the oxidative cychzation of sulfamate esters (e.g., Eq. 52), as well as carbamates (to oxazolidin-2-ones), ° and one can expect further developments that are of synthetic... 

The above results, which are not strongly dependent on the particular value chosen for s, show that about 10% of the trimethylene diradicals lead to propylene, and that the limiting yield of cyclopropane is about 90%. Additional propylene may of course be formed by direct insertion into carbon-hydrogen bonds. 

Much effort has been devoted to activate hydrocarbons, particularly saturated compounds, through the formation of organometallic compounds and transformation of the latter to substituted derivatives. A number of transition-metal complexes have been found to insert into carbon-hydrogen bonds leading to stable alkyl metal hydrides ... 

A widely exploited procedure for bringing about carbenoid reactions of organic mono- and fifem-dihalides is by use of lithium alkyls. Examples are given in equations (11) and (12). Dimeric olefin formation, stereospecific cyclopropane formation from olefins, and insertion into carbon-hydrogen bonds have all been observed in suitable cases, together with further reactions of these products with excess of the lithium alkyl. 

Methylcarbomethoxycarbene. Alkylcarbenes are generally useless as cyclopropane precursors since their singlet states rapidly undergo hydride shifts the prevailing reaction is insertion into carbon hydrogen bonds. For example, direct... 

Silver derivatives containing Tp(CF 2 catalyze the carbene insertion into carbon-hydrogen bonds of cyclic and acyclic hydrocarbons at room temperature. [Ag(Tp CF3 2)(THF)] is more effective... 

The validity of this assumption has been questioned the total amount of insertion products R-CH was found to exceed the possible contribution from radical recombination, as estimated from the yields of R-R and CH ,-CH ). Ring and Rabinovitch have, therefore, suggested that methylene both in the singlet and triplet states inserts into carbon-hydrogen bonds. The calculations of Ring and Rabinovitch were based on the preposition that under their experimental conditions (800-fold excess of nitrogen, approximately 1.6 atm) methylene was entirely in its triplet state. It should be pointed out. however, that similar conditions did not afford the same relative amounts of stereo-isomeric cyclopropanes starting from either cis-or /rans-2-butene ". 

Support for the postulate of a hot methylene- C insertion into carbon hydrogen bonds had already been obtained from observations on the yields of labeled hexanes produced in the irradiation of pentane plus 2-methylpyrazine (Table 11). The statistical nature of the product... 

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