Cyclopentanone, fragmentation reaction

The problem with reactions like this is that both the starting material and product are ketones, so they work cleanly only if the starting material is more reactive than the product. Cyclohexanone is more reactive as an electrophile than either cyclopentanone or cycloheptanone, so it ring expands cleanly to cycloheptanone. But expansion of cyclopentanone to cyclohexanone is messy and gives a mixture of products. We shall come back to diazo compounds in more detail in Chapter 40 diazonium salts will reappear in Chapter 38 where their decomposition will provide the driving force for fragmentation reactions. 

The comments made about the diradical hypothesis with respect to the photochemistry of cyclopentanone are equally applicable to cyclohexanone. Since the formation of none of the products listed in reactions 15-18, and (15,29) is quenched by even 10-20 mm. of oxygen the existence of diradical intermediates in this system is subject to question. The alternative mechanism would be one that causes a concerted split of the ketone molecule in the excited state into two (in the cases of reactions 15 and 16) or three (reaction 17) molecular fragments. Both 16 and 17 are analogous to reactions 3 and 2 in the photochemistry of cyclopentanone and do not involve a shift of hydrogen atom from one... 

The Ferrier (II) reaction is quite efficient to form six membered carbocycles, but is unsuitable to prepare cyclopentitols. Five membered enollactone 14 was converted to the cyclopentanone derivative 16 as a single epimer upon treatment by LiAlH(OtBu)3 (Scheme 4) [41]. Spectroscopic studies established some mechanistic details. Accordingly, the hydride of the reducing agent rapidly added to the carbonyl and formed with the metal a stable alu-minate complex. The carbocydization occurred by protonation followed by fragmentation and aldol type cyclization process. 

Rees and Yelland have reported a fascinating elimination of CO2 from nonadjacent carbonyl groups that occurs both on electron impact and thermolysis Eq. (56). Cyclopentanone p5nrolysis is substantially complicated by radical chain reactions.ii > Nonetheless the three most abundant p5n olysis products, ethylene, carbon monoxide and 1-butene are all represented in the six most intense fragment ions in the mass spectrum of cyclopentanone. 

The pyrolysis of tetramethylenediazirine in the gas phase is a first-order reaction yielding only cyclopentene and nitrogen. Similarly, the treatment of the tosylhydrazone of cyclopentanone with base under aprotic conditions yields cyclopentene as the only hydrocarbon product. Photolysis of this diazirine yields cyclopentene as the principal hydrocarbon product (99.2%), but very small quantities of bicyclo[2,1,0]-pentane (0.3%) and methylenecyclobutane (0.1%) are also formed. In addition, about 0.5% of another hydrocarbon was detected but not identified. Its early position of the chromatogram indicates that it may be a fragmentation product. 

Figure 1 shows the yields of conversion and the products distribution (Cj Cg hydrocarbons, aromatic, polyaroioatics and tar) as a function of reactor temperature for pure cyclopentanone over Il-ZSM-5/bentonite (80/20 Wt.%) catalyst. The conversion is completed at 350 C. The main reaction is a ther.nal decarbonylation of cyclopentanone, giving hydrocarbon fragment that reacts further on the catalytic bed to produce aliphatic, aromatic and polyaroiaatic hydrocarbons. Cyclopentenone which is partially deoxygenated (32%) over H-ZSM-5/bentonite (80/20 Wt.%) at 450 C, can be completely converted... 

Cyclopentanone can be deoxygenated in high yield to hydrocarbons over H-ZSM-5 above 350 C. The main reaction is a thermal decarbony-lation of cyclopentanone to give CO and fragment that can react further on the catalytic bed to produce aliphatic, aromatic and polyaromatic hydrocarbons. Cyclopentenone with ( /C)aff 0 8 is more difficult to deoxygenated. The addition of methanol raises the (H/C)eff ratio and permits the complete deoxygenation over H-ZSM-5. 

Synthesis of 2,2,3-trisubstituted cyclopentanone (633) has been realised through 1,4-asymmetric addition reaction of 2-methylcyclopent-2-ene-l-one (629) to chiral phosphonamide (630). Subsequent allq lation with methyl bromoacetate (631) afforded 2,2,3-substitued cyclopentanone derivative (632) with three stereocentres in very high stereo-seleetivity (>90%). Finally, removal of the covalently bonded chiral auxiliary using oxidative methods provided o-ring fragment of 9,11-seeosterols (633) in 79% yield and with the RRS configuration (Scheme 184). ... 

The fast pyrolysis decomposition of cellulose starts at temperatures as low as 150°C. Pyrolysis of cellulose below 300°C results in the formation of carboxyl, carbonyl, and hydro peroxide groups, elimination of water and production of carbon monoxide and carbon dioxide as well as char residue (Evans and Milne, 1987). Therefore low pyrolysis temperatures will produce low yields of organic liquid yields. Fast pyrolysis of cellulose, above 300°C, results in liquid yields up to 80 wt.%. Cellulose initially decomposes to form activated cellulose (Bradbury et al., 1979). Activated cellulose has two parallel reaction pathways, depolymerization and fragmentation (ring scission). The main products from each reaction pathway are rather different as ring scission produces hydroxyacetaldehyde, linear carbonyls, linear alcohols, esters, and other related products (Bradbury et al., 1979 Zhu and Lu, 2010 Lin et al., 2009) and depolymerization produces monomeric anhydrosugars, furans, cyclopentanones, and pyrans and other related products (Bradbury et al., 1979 Zhu and Lu, 2010 Lin et al., 2009). Each reaction pathway is independent and is influenced by pyrolysis temperature and residence time (Bradbury et al., 1979). 

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