Lead alkyls thermolysis

Lactone intermediates, 94,127, 228 Lateral overlap, orbitals, 9 Lead alkyls, 301 anti-knock, 305 thermolysis, 301, 304, 324 Leaving groups, 98, 99, 127,139, 237 ability of, 98, 251... 

Methyl free radicals, generated either by thermolysis of lead tetracetate in acetic acid solution (401) or by radical cleavage of dimethylsulfoxide by H2O2 and iron (II) salts (408), afford 2- and 5-methylthiazole in the proportion of 86 and 14%, respectively, in agreement with the nucleophilic character of alkyl free radicals and the positive charge of the 2-carbon atom of the thiazole (6). 

Extrusion of sulphur dioxide from cyclic systems leading to dienes has proved to be a synthetically useful reaction112. Thermolysis of cis- and fraw,s-2,5-disubstituted sulp-holenes, which can be readily obtained through regio- and stereoselective alkylation, proceeds in a stereospecific manner affording 1,3-dienes of high stereochemical purity, as predicted by symmetry rules (equations 68 and 69)113. On the other hand, a photochemical process is not completely stereospecific (equation 68)114. 2,5-Dialkylative cyclization... 

In contrast, thermolysis of the telluroformates at 160°C in the dark leads to the formation of alkyl aryltellurides in good yields, presumably through the transient oxyacyl... 

Proposed General Explanation for Alkyl Hydride Instability. The advantage of suggesting a five-coordinate acyl hydride as the reactive intermediate in Os(CO)4(H)CH3 thermolysis is that it leads to a general explanation of elimination processes of this type. That general explanation contains the following elements ... 

In contrast to the thermolysis reactions described above, photolysis of perfluoro (alkyl-pyridazines) leads to high yields of pyrazines.40-42 Thus, irradiation of pyridazines 33 with unfiltered light in the vapor phase gives pyrazines 34.40... 

The free radical substitution reactions, other than phenylation, of pyridine and its derivatives have received but scant attention. Alkylation of pyridine itself has been studied briefly, the alkyl radicals being generated either by the thermolysis of diacyl peroxides or of lead tetraacetate in acetic acid, or by electrolysis of the carboxylic acid precursor (for summary, see Norman and Radda369). Most of the available results are summarized in Table XIV. These figures on isomer ratios are not very reliable since the analyses were carried out by... 

Addition of H[BF4] to 4-amino-l-metalla-l,3-dienes ( )-96 in ether leads to precipitation of a stable dia kyliminio(alkyl)carbene complex 106, which has been characterized by X-ray analysis. Compound 106 is more reactive toward insertion at the M=C bond than its precursor ( )-96. Thus, a marked enhancement of reactivity is achieved by protonation of 4-amino-1-metalla-l,3-dienes. Addition of LiBr to compound 106 and thermolysis... 

Azo compounds can exist in either the cis or trans form. It is reasonable to assume that the azoalkanes in Table 5-8 exhibit the trans configuration. Contrary to the small solvent effects obtained in the decomposition of trans -azoalkanes, the thermolysis of definite cu-azoalkanes reveals a significant solvent influence on rate. Thermolysis of ah-phatic symmetrical cw-tert-azoalkanes can lead either to the corresponding trans-tert-azoalkanes, presumably via an inversion mechanism, or to tert-alkyl radicals and nitrogen by decomposition via a free-radical transition state [192]. An example of the first type of reaction is the Z)I E) isomerization of [1,1 jazonorbornane. Its rate is virtually solvent-independent, which is consistent with a simple inversion mechanism [565, 566], The second reaction type is represented by the thermal decomposition of cis-2,2 -dimethyl-[2,2 ]azopropane, for which a substantial decrease in rate with increasing solvent polarity has been found [193] cf Eq. (5-60). 

The oxidative cleavage of [ CoX2(i7-C5Me5) 2] (X = Cl or Br) in water to give [Co(aq) (i7-C5Me5)] has been studied by cyclic voltammetry 213). Details 214) have been presented of the reactions of [ Co(/t-CO)Cp 2] with alkyl halides thermolysis of the products, namely [ CoR(CO)Cp 2], leads to carbon-carbon coupling (Section... 

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