Methylene insertion into

The highly reactive species methylene inserts into C—H bonds,both aliphatic and aromatic,though with aromatic compounds ring expansion is also possible (see 15-62). This version of the reaction is useless for synthetic purposes because of its nonselectivity (see p. 248). This contrasts with the metal carbene insertion reaction, which can be highly selective, and is very useful in synthesis. Alkylcarbenes usually rearrange rather than give insertion (p. 249), but, when this is impossible. 

Methylene insertion into C—H bonds is believed to be concerted for the singlet species and stepwise for the triplet.<164,156) The C—H insertion of methylene into the 14C-labeled isobutylene shown below results in 92% unrearranged isopentenes and 8% rearranged isopentene [Eq. (11.22)]. Assuming that an additional 8% of the unrearranged isopentene arises from the stepwise addition, it is clear that 84% of the insertion products result from insertion by singlet methylene and 16% by triplet methylene ... 

An interesting report has been made of methylene insertion into the P-C linkage of a-(acyloxy)iminoalkylphosphonates derived from carbohydrates.181 This reaction system, using diazomethane, allows extension of the chain by a single carbon atom, with that atom (methylene group) attached directly to the phosphorus. 

Both stereoisomers of a 4-(a-arylethylidene)-5(477)-oxazolone 441 and 443, undergo stereospecihc hydrolysis-methanolysis to furnish the corresponding (Z) and (E) isomers of 2-acetylamino(or benzoylamino)-3-aryl-2-butenoic acid or methyl ester, 442 and 444, respectively (Scheme 7.146). ° The requisite starting oxazolones were prepared by condensation of an acetophenone with an acylglycine or by methylene insertion into the vinyl C—H bond of a 4-arylidene-5(4//)-oxazolone. 

These include the four possible diastereomeric spirocyclopropane derivatives 633, 685, 634, and 686 resulting from methylene insertion into the double bond and a spirocyclopropane 687 derived from methylene insertion into the double bond of a homologated 5(4f/)-oxazolone. The amount of 687, the cis/trans selectivity and both the cis and trans diastereoselectivities depend on the reaction conditions. Use of nonpolar solvents avoids formation of 687. In addition, the cis/trans selectivity and both cis and trans diastereoselectivities are very high such that the major compound 633 can be isolated in 75% yield (Scheme 7.216). ... 

Methylene insertion into a silicon sihcon bond is also possible for a reactive Si-Si bond (equation 36). Insertion reactions of divalent silicon species, silylene, also occur to the same substrate. Silylene forms a new silicon-carbon bond with a variety of substrates, which will be described later. 

Both of these suggestions are defective because of the absence of methane (route A) and the much greater quantities of TMMD produced compared with DMA (route B with Reaction 19 as the precursor of methylmethylene imine). A further route to TMMD could be provided by methylene insertion into the NN bond of TMH. This, though theoretically feasible, seems unlikely and requires the production of methylene from dimethylamino radicals by a surface reaction. The radical decomposition reactions (29 and 30) proposed by Gesser, MuUhaupt, and Griffiths (15) are not confirmed by our results. 

Methylene insertion into the Au—S bonds of the heterobimetallic complex 501 results in the formation of the larger ylide ligands in 502 (280). 

I) Zinc. Diazomethane with Znl2 in EtjO gives ICHjZnI and, with xs CH2N2, (ICH2)2Zn i.e., methylene insertion into the Zn-halide bond oceurs ... 

The catalysts derived from supported iron clusters exhibit in Fischer-Tropsch synthesis a high selectivity for propylene. Those catalysts are also selective for the stoechiometric homologation of ethylene to propylene and of propylene to n and iso butenes. The results are explained on the basis of a new mode of C-C bond formation which implies < - olefin coordination to surface methylene fragments or methylene insertion into a metal alkyl bond. 

Direct concerted insertion is characteristic of singlet carbene and the three-center cyclic transition state 139 suggested by Doering and Prinzbach" has been supported by kinetic data" and theoretical studies." Singlet methylene inserts into C-H bonds of hydrocarbons in a statistical fashion" [Eq. (6.128)] ... 

Palladium-based catalysts also bring about cyclopropanations in high-yield. With palladium acetate/CHjNj, styrene , unactivated terminal olefins strained olefins , 1,3-dienesan enamine , as well as a,3-unsaturated carbonyl compounds have been cyclopropanated (Table 1). Contrary to an earlier report, the reaction also works well with cyclohexene if the conditions are chosen appropriately it seems that the notniyst is rapidly deactivated in the presence of this olefin >. Trisubstituted a,p-unsaturated carbonyl compounds were found to be unreactive, and the same is true for the double bonds in diethyl fumarate, maleic anhydride, coumarin and 1,3-dimethyluracil. Whereas the latter two were totally unreactive, [3-1-2] cycloaddition of diazomethane gave pyrazolines in the former two cases. The last entry of Table 1 shows that an allyl alcohol function can still be cyclopropanated, but methylene insertion into the O—H bond is a competing process. 

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... 

RELATIVE RATES OF METHYLENE INSERTION INTO ETHERS (Photolysis of Diazomethane)... 

Similarly, sulfenimino-P-lactam 205 [107] reacted with diazomethane to give y-lactam 206 by methylene insertion into the C-6/C-7 azetidinone bond (Scheme 58). A spiro-aziridine intermediate was probably formed [106]. Sulfen-amide cleavage initiated by triphenylphosphine followed by acylation and ester deprotection led to the acid 207 which does not have any significant antimicrobial or p-lactamase inhibitory activity [106]. 

Methylene generated from diazomethane is so reactive that it inserts into C-H bonds as well as C=C bonds. For example, in the reaction of propene with diazomethane-generated methylene, several side products are obtained (Scheme 5.44). Methylene inserts into both primary and tertiary C-H bonds whereas carbomethoxymethylene reacts almost solely at the tertiary position (Scheme 5.45). 

However, in these reactions complex mixtures of unusual side products resulting from an oligomethylenation have been also isolated. The products can be explained by invoking intermediates like 29, which undergo methylene insertion into the metal carbon bond (Scheme... 

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