Cyclopentanones carbonylation

Heat-induced degradation leads to formation of furans, pyrones, cyclopentanones, carbonyls, pyrroles and acids which possess objectionable flavor qualities at low concentrations. Most have odors typically described as caramel-like and burnt sugar-like. 

Aflatoxicol occurs as one of the metabolic transformation products of aflatoxin Bi(i) via the reduction of the cyclopentanone carbonyl moiety81. The isolation and structure were done by Detroy82, and the toxin identified as (17). 

The methanol adduct produced by the photoisomerization of isocolchicine in methanol exhibited a styrene chromophore and a cyclopentanone carbonyl group (38) no olefinic protons were detectable in the NMR-spectrum. Catalytic hydrogenation resulted only in reduction of the carbonyl group acid hydrolysis of the dihydro compound (with... 

Heathcock et al. have employed the MM2 force field in their study of fawcettimine (41 R = H) and derivatives <89J0C1548>. The calculated energy difference of the Y-acetyl epimers (41) and (42) (R = Ac) was 1.4 kcal mol (5.9 kJ mol ), which compares with the experimentally determined value of0.41 kcal mol (1.72 kJ mol ). Fiuther calculations were consistent with the experimental data concerning the formation of intramolecular carbinolamines from both epimers fawcettimine (41 R = H) formed a carbinolamine at the cyclohexanone ring, whereas 4-epifawcettimine (42 R = H) formed a carbinolamine at the cyclopentanone carbonyl. Maryanoff et al. have studied the... 

Potassium cm bonate acts as a base by producing the abstraction of a proton on an a position of the cyclopentanone carbonyl. The resulting anion evolves by expulsion of the alkoxide in the p position by an EicB mechanism. 

Titanium(IV) is a powerful but selective Lewis acid which can promote the coupling of allylsilanes with carbonyl compounds and derivatives In the presence of titanium tetrachlonde, benzalacetone reacts with allyltnmethylsilane by 1,4-addition to give 4-PHENYL-6-HEPTEN-2-ONE. Similarly, the enol silyl ether of cyclopentanone is coupled with f-pentyl chloride using titanium tetrachlonde to give 2-(tert-PENTYL)CYCLOPENTANONE, an example of a-tert-alkylation of ketones. 

Experimental evidence, obtained in protonation (3,6), acylation (1,4), and alkylation (1,4,7-9) reactions, always indicates a concurrence between electrophilic attack on the nitrogen atom and the -carbon atom in the enamine. Concerning the nucleophilic reactivity of the j3-carbon atom in enamines, Opitz and Griesinger (10) observed, in a study of salt formation, the following series of reactivities of the amine and carbonyl components pyrrolidine and hexamethylene imine s> piperidine > morpholine > cthyl-butylamine cyclopentanone s> cycloheptanone cyclooctanone > cyclohexanone monosubstituted acetaldehyde > disubstituted acetaldehyde. 

In the mixed Claisen reaction of cyclopentanone with ethyl formate, a much higher yield of the desired product is obtained by first mixing the two carbonyl components and then adding base, rather than by first mixing base with cyclopentanone and then adding ethyl formate. Explain. 

Similar to cyclohexanones, substituted cyclopentanones also adopt a conformation with the substituents in a sterically favorable position. In the case of 2-substituted cyclopentanones 1 the substituent occupies a pseudoequatorial position and the diastereoselectivity of nucleophilic addition reactions to 1 is determined by the relative importance of the interactions leading to predominant fra s(equatorial) or cw(axial) attack of the nucleophile. When the nucleophile approaches from the cis side, steric interaction with the substituent at C-2 is encountered. On the other hand, according to Felkin, significant torsional strain between the pseudoaxial C-2—H bond and the incipient bond occurs if the nucleophile approaches the carbonyl group from the trans side. 

Another example of the application of high pressure in the field of domino transformations has been revealed by Brinza and Fallis, representing a carbonylation/cy-clization procedure [4]. Thus, when hydrazones 10-12, bearing a bromine atom, are subjected to standard radical conditions under a high-pressure atmosphere of carbon dioxide, cyclopentanones 10-16 and 10-17 are smoothly produced in good yields (Scheme 10.3). 

As described above, our synthetic strategy involves the convergent construction of the central cyclopentanone ring with a carbonylative cross-coupling reaction and a photo-Nazarov cyclization reaction (Chart 2.2). The electrophilic coupling component 51 was synthesized by an intramolecular Diels-Alder reaction [34] and the nucleophilic coupling component 52 by a vinyiogous Mukaiyama aldol reaction [35]. 

Condensation of [3- or "y-amino alcohols with aldehydes or ketones RR CO gives the product 27. In solution the position of the equilibrium varies with R and R, and with the solvent (73). When the carbonyl reactant is a substituted benzaldehyde, the solid is found (IR, KBr) to comprise molecules of the open-chain structure 27a, whereas aliphatic aldehydes and ketones give crystals of dihydro- 1,3-benzoxazines, 27b. An interesting case is that of the condensation product of o-hydroxybenzylamine with cyclopentanone, for which McDonagh and Smith (73) suggest that ring and chain tautomers coexist in the solid. 

Me,SiCl (6.5 g, 60 mmol) in CCl4 (10 ml) is added to the semicarbazone (30 mmol), NaN02, or NaNOj (42 mmol), TEBA-Cl (0.34 g, 1.5 mmol) in CCI4 (20 ml) and the mixture is stirred for 3 h at room temperature. The mixture is filtered through silica and evaporated to yield the carbonyl compound (e.g. EtCOMe, 78% 1-BuCOMe, 84% cyclopentanone, 83% cyclohexanone, 78% PhCHO, 95% PhCOMe, 80% Ph2CO,... 

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