Cyclo-pentene, 3-methyl

Cyclo-pentene, 3-methyl CH3-a/do-CsH7 71.5 2 299.2 8.4 Derived from AfH° in ref. 1996N1ST... 

Three compounds appear to be of particular importance in flavor volatiles identified by Ching (3) from beef diffusate or dried beef. These are 2-hydroxy-3-methyl-2-cyclo-penten-l-one, 4-hydroxy-5-methyl-3(2H)-furanone and 4-mercapto-5-methyl-tetrahydro-3-furanone. 

Fig. 3.5. Relationship between log (retention time) and boiling point for a range of hydrocarbons on squalane at 43°C. A, aliphatics (and benzene) B, alicyclics, 1-4 = C5-Cg n-alkanes 5 = 2-methyl-butane 6 = 2-methylpentane 7 = 2,3-dimethylbutane 8-12 = C4-C8 1-olefins 13,15,17 = trans-(but-2-ene, pent-2-ene and hept-2-ene) 14,16,18 = e/s-(but-2-ene, pent-2-ene and hept-2-ene) 19 = 2-methylbut-l-ene 20 = 2-methylpent-l-ene 21 = 4-methylpent-l-ene 22 = 2-methylbut-2-ene 23 = cyclopentane 24 = cyclohexane 25 = methylcyclopentane 26 = methylcyclohexane 27 = cyclo-pentene 28 = cyclohexene 29 = 4-methylcyclohexane 30 = 1,3-butadiene 31, 32 = trans- and cis-1,3-pentadiene 33 = diallyl 34, 35 = trans- and c s-2-methyl-l,3-pentadiene 36 = cyclopentadiene ...

Stetter H, Kuhhnann H, Haese W (1987) The Stetter reaction 3-methyl-2-pentyl-2-cyclo-penten-l-one (dihydrojasmone) (2-cyclopenten-l-one, 3-methyl-2-pentyl-). Org Synth 65 26-31 Stetter H, Kuhhnann H (1991) The catalyzed nucleophilic addition of aldehydes to electrophilic double bonds. Org React 40 407 96... 

Alpha diketones 3-methyl-2-hydroxy-2-cyclo-penten-l-one a burnt sugar, roasted, lingering aroma. 

In the case of cyclopentene polymerization, the insertions at secondary alkyls are the only possible mode of chain growth no insertions adjacent to tertiary carbons are observed. For substituted cyclo-pentenes, there are more options in the polymerization. For instance, with 4-methylcyclopentene, insertion generally takes place on the unsubstituted side of the ring. This leaves a cis-C—H bond available for chain walking to the methyl group. The next insertion takes place at the primary carbon atom, giving a methylenecyclopentane polymer as illustrated in eq 8. A similar behavior is observed for... 

In 1972 Olah attempted to observe directly a trishomocyclopropenyl cation postulated in all the works described above. However, the ionization of cis-3-bicyclo[3,l,0]hexanol in FSOjH—SbFj—SOjFCl resulted only in a 3-methyl-cyclo-pentene-2-yl cation. The primarily formed bicyclic cation seems to be very unstable. 

Jsisi of 4.6 Hz has been observed in the Si NMR spectrum of 2,5-bis(9-borabicyclo[3.3.1]non-9-yl)-2,5-bis(trimethylsilyl)-l,l-dimethyl-l-sila-3-cyclo-pentene and a Vsisi of 5.1 Hz in that of 2,5-bis(9-borabicyclo[3.3.1]non-9-yl)-2,5-bis(trimethylsilyl)-1 -methyl-1 -sila-3-cyclopentene. ... 

Methyl-l. 1-pentamethyIen-cyclo> penten.(4).on-(3)-tiicarb[Pg.1184]

Hulupone or 2-(3-methylbutanoyl)-5,5-bis(3-methyl-2-butenyl)-3-hydroxy-2-cyclo-pentene-1,4-dione (56, Figs. 23 and 83) is a yellow oil with a boiling point of 110°C at 10 mm Hg. It forms a quinoxaline with 1,2-diaminobenzene (melting point 110 C) (4). The pK/ value in methanol water 1 1 is 2.6 and the molecular formula C20H28O4. The UV absorption maxima are situated at 277 nm in acidic methanol and at 254 nm and 310 nm in alkaline methanol. These features are ascribed to an enolized cyclopentane-1,2,4-trione system (5). The H NMR spectrum shows the absorption signals for the protons of a 3-methylbutanoyl group and two 3-methyl-2-butenyl side... 

Some exceptions to the general rules occur. Cyclopentene is completely combusted, undoubtedly because of the high reactivity of cyclo-pentadiene. 4,4-Dimethyl-1-pentene is expected to produce an unsaturated aldehyde, but instead 2,3-dimethylpentadiene is the initial product. A methyl shift from a quarternary carbon is apparently easy, permitting formation of a diene instead of the oxygenated compound. 3,3-Dimethyl-l-butene is not expected to react at all under the general rules, but here also a methyl shift occurs so that diene, olefin aldehyde, diene aldehyde, and diene dialdehyde are formed. The reactivity of the latter olefin relative to 1-butene, measured by oxidation of a mixture at low conversion, was 0.21, while that of 4,4-dimethyl-1-pentene was 0.75. These reactivities suggest that isomerization occurs before reaction for 3,3-dimethyl-l-butene, while isomerization probably occurs after the aUyl intermediate is formed in the case of the pentene. 

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