Alkanes methylene insertion into

The oxygen atom of aliphatic ethers has a small promoting effect on methylene insertion into neighboring carbon-hydrogen bonds . By analogy with the behavior of alkanes, discrimination appears to be more pronounced in the... 

The reactivity between a tertiary C-H site and a sterically accessible, secondary C-H site is relatively even in the reactions catalyzed by TpBf3Cu. This can be seen in the reaction with 2-methylpentane (Equation (7)),38,49,56 which gave rise to a mixture of only two products. No insertion into the methyl or the sterically crowded methylene C-H bonds was seen. The C-H insertion has the possibility of selectively functionalizing relatively complex alkanes. An impressive example is the C-H insertion to 1 (Equation (8)).56 A mixture of two alkylation products derived from insertion at the tertiary C-H bonds was obtained. This transformation has been extended to the selective functionalization of hydrocarbon polymers.75... 

The oxidation of organic substances by cyclic peroxides has been intensively studied over the last decades , from both the synthetic and mechanistic points of view. The earliest mechanistic studies have been carried out with cyclic peroxides such as phthaloyl peroxide , and more recently with a-methylene S-peroxy lactones and 1,2-dioxetanes . During the last 20 years, the dioxiranes (remarkable three-membered-ring cyclic peroxides) have acquired invaluable importance as powerful and mild oxidants, especially the epoxidation of electron-rich as well as electron-poor alkenes, heteroatom oxidation and CH insertions into alkanes (cf. the chapter by Adam and Zhao in this volume). The broad scope and general applicability of dioxiranes has rendered them as indispensable oxidizing agents in synthetic chemistry this is amply manifested by their intensive use, most prominently in the oxyfunctionalization of olefinic substrates. 

Singlet NH inserts into the CH bonds of hydrocarbons, much like singlet methylene (see Chapter 7 in this volume). Triplet NH abstracts hydrogen atoms from hydrocarbons to form aminyl (NHp radicals and alkyl radicals in the same manner as triplet methylene, in spite of the fact that the reactions of CH2 are exothermic, whereas some reactions of NH are endothermic, depending on the alkane Absolute rate constants for many of these processes have been measured in the gas phase. However, the gas-phase chemistry of methylene is much more developed than that of imidogen. ... 

As previously mentioned, the belt of glycolurils that inserts into the capsule increases the length by some 7 A and the volume by nearly 50% [83]. In the expanded capsule tetradecane relaxes into an extended conformation and this is evident from changes in the H NMR spectrum. The NMR signals move downfield as the methylenes of the alkane move away from the walls and toward the center of the structure. The different NMR spectra of tetradecane in the original vs the expanded capsule is shown in Fig. 16. 

Photolysis (200-260 nm) of diazomethane (CH2N2) produces highly reactive methylene (rCHj), which can insert into primary, secondary, and tertiary C-H bonds of an alkane with almost equal ease, as well as undergo addition to double bonds. The eyclopropanation of alkenes can, however, be achieved by carrying out the photolytic decomposition of diazomethane in the presence of metal salts. Palladium(II) acetate has been reported to be a very effective catalyst for the eyclopropanation of alkenes using diazomethane vide infra). 

Concurrently, Noels had reported that rhodium carboxylates smoothly catalyze the intermolecular C—H insertion of ethyl diazoacetate into alkanes. Following up on this report, Taber demonstrated that the open chain a-diazo 3-keto ester (60) cyclizes smoothly under rhodium acetate catalysis to give the corresponding cyclopentane (61 equation 24). In contrast to the copper-mediated cyclization cited above (equation 22), the six-membered ring product is not observed. The insertion shows significant electronic selectivity. Although there is a 3 1 statistical preference for methyl C—H, only the methylene C—H insertion product (61) is observed (equation 24). 

The application of both criteria to gas-phase reactions is complicated further by the formation of vibrationally excited products. Both the insertion and addition reactions of methylene are exothermic by approximately 93 kcal. mole (based on recent estimates of AH (CH2) = 94 kcal.mole" ). Vibrationally excited alkanes and alkenes may dissociate into free radicals, and excited cyclopropanes may undergo structural and geometrical isomerizations unless collisionally stabilized . The occurrence of hot molecule reactions excludes any reasonable estimation of singlet and triplet methylene fractions. The data presented in the following paragraphs have been taken from experiments at high-pressures", which are thought to ensure complete collisional deactivation of excited reaction products. 

Insertion of a carbonyl between two methylene groups transforms an n-alkane into an alkanone. Since the group volume and bond angle to neighboring carbon atoms of a carbonyl are only c. 15% and c, 4° larger, respectively, than those of a methylene [37-40], the intrinsic shapes and sizes of alkanes and alkanones with the same number of carbon atoms are very similar. On that basis, they should form similar solid phase structures differences may be attributable to the opposite... 

A series of experiments on the reactivity of metal ions with nitriles, RCN, led to the discovery of the remote functionalization mechanism. The initial interaction of the metal ion involves coordination at the nitrile group. The insertion of the metal atom into a C—or C—C bond occurs only after the alkyl chain becomes long enough (at least three or four methylene groups) to interact with a remote bond. The dissociation of the metal-hydride or metal-alkyl intermediate results in a loss of H2 alkene or alkane molecules, depending on the structure of the hydrocarbon group R. 

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