Carbon methylenation

We considered the polymer chain could be formed by either primary or secondary insertion. Primary insertion is when the monomer forms a bond with the methylene group to the catalyst metal and secondary insertion is where the metal and monomer form a bond with the propylene methine group. Ethylene must always add by primary insertion, but propylene can add either way. And, in fact, the presence of the ag secondary carbon shows the presence of a two carbon methylene sequence which can occur only if both types of insertion are in force. 

To carry out tethered [3-i-2]-cycloadditions Nakamura et al. developed the new annulating reagents 123 [109, 110]. The reagents carry, in one molecule, two cyclopropenone acetals that are connected with an n-carbon methylene tether. Upon thermolysis in the presence of Cjq, the reagent undergoes [3-i-2]-cycloaddition reaction twice in a regio- and stereoselective manner to give Q- and C2-symmetrical bisadducts with cis-l - and cis-3-addition patterns, respectively. The selectivity varies... 

Alkylation of acetylacetone chelates is generally unsuccessful, but carbon—methylene bonds can be formed by chloromethylation,279 reaction with ethyl diazoacetate,287 reaction with thioacetals288 (equations 64, 65 and 66) and by the Mannich reaction (Scheme 73).279 The Mannich base can be quatemized with methyl iodide and converted by cyanide ion into a cyanomethyl-substituted chelate. 

Ziegler and co-workers (216, 217) have described a new approach to the quebrachamine skeleton involving internal cyclization of an acetic acid side chain to a 2-unsubstituted indole. The key intermediate is the disubstituted piperidine 466, which is treated with indolyl-3-acetyl chloride in aqueous sodium carbonate-methylene chloride to afford a lactam ester, 467. 

The proton ENDOR pattern of nitrile hydratase shows strong, nonexchangeable protons, with A values around 15 MHz, assigned to the )8-carbon methylene protons of cysteine ligands (Fig. 17). In Fig. 17 again... 

Formaldehyde readily polymerizes to a high polymer, with a chain of alternating carbon (methylene groups) and oxygen atoms ... 

The material was also studied in nonaqueous electrolytes such as acetonitrile propylene carbonate methylene chloride and ethanol ° Mn acetonitrile,... 

FIGURE 8.6. HMQC spectrum oflimonin obtained on a JEOL ECS spectrometer at 100 MHz spectrometer, along with the assignments of all the protons and carbons. Methylene protons are chemically eSfferent, two distinct cross peaks were observed corresponding to axial and equatorial protons. Traces of one-dimensional H spectrum (top) and DEPT 135 spectrum (right side) shown. For clarity, DEPT-135 spectra CH and CH are on positive in blue, and CH2 negative, in red, are also shown. The proton labels with a refer to axial protons, and labels with e" refer to equatorial protons. 

The three subspectra show good separation (Fig. 6.20). In the CH spectrum, the multiplet at 29 ppm is a solvent impurity. The peaks at 44 and 52 ppm result from methine carbons. From the CH2 subspectrum, the signal at 35 ppm is associated with the methylene carbons. Methylene subspectra were obtained from four copolymers with different compositions to allow the comonomer sequence assignments to be made for the observed resonances. 

The magnitude of is related to the strength of the static dipolar interactions between the carbons and protons. Tch should be less than 0.13 ms for a rigid methylene group [71]. In general, TCH values decrease in the following order non-protonated carbons > methyl (rotating) carbons > methylene carbons > protonated aromatic-aliphatic methine carbons > methyl (static) carbons. 

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