Cyclobutanone pyrolysis

Thus, addition of dichloroketene to cyclohexene gave 8,8-dichlorobicyclo[4.2.0]octan-7-one in 39% yield which underwent dehalogenation upon treatment with zinc in acetic acid at room temperature for 24 hours to give the corresponding cyclobutanone. Pyrolysis of the dry lithium salt of its tosylhydrazone at 120-180°Cat0.1 Torr produced a 2 1 mixture of isomeric methylenecyclopropanes 42 and 43 in 50% yield. 

In marked contrast to that of cyclobutanes, the cycloreversion of cyclobutanones to ethene and ketene88 is most probably a concerted process.89-94 For example, the fact that the pyrolysis of 2-propylcyclobutanone (13) at 350 °C gives ethene and pent-l-ene in the ratio of 3.8 1 is not easily explained by a diradical mechanism.90 This transformation presumably involves two competing cycloreversion reactions. As expected for a concerted process, the conversion through the less sterically congested transition structure is favored. For this reason, ethene is generated as the major alkene.90... 

Cyclobutanone has been deoxygenated to give carbon monoxide and cyclobutylidene by reaction with atomic carbon atoms generated from the pyrolysis of 5-tetrazolyldiazonium chloride (31). As expected, cyclobutylidene (2) rearranges under these conditions to afford, in a total yield of only 3.8 %, a mixture of methylenecyclopropane (3), cyclobutene (32) and buta-l,3-di-ene (33) in a ratio of 66 10 24.12... 

The first recorded cyclopropyl acyl silane (69) was generated by vapour phase pyrolysis of a pyrazoline derived from a,/)-unsaturated acyl silane by 1,3-dipolar cycloaddition of diazomethane (vide supra, Section DTE)141. Exposure of 69 to titanium tetrachloride induced ring expansion to give the cyclobutanone in 75% yield (Scheme 113). 

The kinetics of the decomposition of cyclopentanone are complex and definitely differ from those of cyclobutanone as well as from those of other ketones. In spite of the uncertain mechanism, it may be stated that this reaction is, in many respects, similar to the pyrolysis of cyclopentane. In both cases, dehydrogenation and rupture of the ring take place as simultaneous processes. 

Ring contraction of cyclobutylidenes is known, but not so widely explored. Thus, pyrolysis (200°C) or irradiation of the lithium or sodium salt of cyclobutanone tosylhydrazone (262) gave the 2-vinylcyclobutylidene (263) which then rearranged mainly to ring contraction products (equation 181). 

Acetone, butanone, cyclobutanone and similar ketones have been used to prepare Schiff bases from long-chain amines, aromatic amines, diamines, anriino-phenols and catecholamines in biological media [29-34], and from hydrazines in air [35], prior to separation by GC. When electron capture detection was used, penta-fluorobenzaldehyde was the chosen reagent. This procedure was applied to the analysis of traces of amines in water samples [36] and biological extracts [37,38], as well as hydrazine in tobacco smoke, technical maleic hydrazide and pyrolysis products [39]. 

To test for the intermediacy of free carbenes in the decomposition of metal-carbene complexes, the thermolysis of the 2-oxacyclopentylidene complex XVII was studied (Anderson and Casey, 1975). 2-Oxacyclopentylidene has been generated by pyrolysis of the sodium salt of butyrolactone tosylhy-drazone and shown to rearrange to give both dihydrofuran and cyclobutanone (Agosta and Foster, 1972). The thermolysis of XVII in decalin at 180° for 15... 

Miscellaneous. a-Organylthioketones and esters can be prepared by treatment of enolates with RSSR (compare ref. 202), pyrolysis then giving a/S-unsaturated carbonyl compounds. If the same reaction is applied to cyclobutanones, and conditions chosen such that bis-sulphenylation and ring cleavage occur, a convenient route to thioacetals of y-ketoesters is obtained (Scheme 32). ... 

Ethylene, keten, cyclopropane, and carbon monoxide were the products observed in a kinetic investigation of the pyrolysis of cyclobutanone in the temperature range 360.0—406.3 °C. The activation parameters and product analyses were better accommodated by concerted mechanisms than by reactidns through biradical intermediates. Pyrolysis of 2-propylcyclobutanone (388) gives ethylene and pent-l-ene in the ratio 3.8 1 at 350 "C, and a biradical mechanism cannot easily account for this result. It is quite compatible with... 

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