Cyclopentane reactions

A study of the stoichiometric cyclopentane reaction over Ta-H has revealed that tantalum hydride very easily achvates cyclopentane, forming the corresponding cyclopentyl derivative. However, the latter is very quickly transformed into a cyclo-pentadienyl compound, as shown by NMR and EXAFS studies. This cyclopenta-dienyl derivative presents no achvity in alkane hydrogenolysis ... 

The effect of sulfur and Pt-Re interaction on coke deposition were studied at high pressure (15 bar) in the course of cyclopentane reaction at 450°C for 16 h (Table 4). The catalyst prepared by catalytic reduction and activated by direct reduction (close Pt-Re interaction), deposits less coke than catalysts activated by calcination followed by reduction (weak Pt-Re interaction). 

The deactivation of the three same catalysts by carbon deposits was also studied in the course of the coking reaction with cyclopentane. Contrary to the results obtained for the isobutane dehydrogenation reaction, the carbon content of catalysts submitted to the cyclopentane reaction at 500°C for I h decreases following the sequence SI Pt-Sn > coimpregnated Pt-Sn > Pt/Al203 (Table 3). The analysis of the TPO curves shows that the behavior of the SI catalyst arises... 

Influence of the Acid Function.- It has been shown that most of the coke deposition on the bifunctional naphtha reforming catalyst occurs on the acid function. Barbier et al. showed the importance of the acid sites of the support by performing TPO studies of coke from cyclopentane reaction on three catalysts Pt(0.59)/AI2O3 and the same catalyst modified by the addition of H BO and by the addition of KOH. The neutralization of basic sites of alumina by H3BO3 modified the quantity and localization of coke very little, whereas the neutralization of acid sites by KOH produced a decrease of 90% of the quantity of coke deposited on the support. Thus it is apparent that the polymerization leading to coke is essentially of an acid nature. A similar effect was observed in the coking produced... 

In 2012, Cobb and co-workers [41] developed a cyclopentanation reaction between nitrostyrenes and E-nitro-a, 3-unsaturated esters (62). The reaction is catalyzed by bifunctional tertiary amine-thiourea catalysts, affording the highly substituted cyclohexanes 63 in good yields and enantioselectivities (Scheme 10.19). 

Seven-membered Rings.—Whereas pyrolyses of 5-acetoxymethylcycloheptene at 350 °C in a flow system gave mixtures of bi- and tri-cyclic products, pyrolysis in a sealed tube gave a mixture of 5-methylenecycloheptene and l-methylene-3-vinyl-cyclopentane. " Reactions of cyclohepta-2,6-dienone with substituted hydrazines, hydroxylamines, and carbohydrazines, gave the adducts (217). ... 

Ibrahem, L, Zhao, G. L., Rios, R., Vesely, J., Sunden, H., Dziedzic, P., Cordova, A. (2008). One-pot organocatalytic domino MichaeFalpha-alkylation reactions direct catalytic enantioselective cyclopropanation and cyclopentanation reactions. Chemistry - A... 

Some straightforward, efficient cyclopentanellation procedures were developed recently. Addition of a malonic ester anion to a cyclopropane-1,1-dicarboxylic ester followed by a Dieckmann condensation (S. Danishefsky, 1974) or addition of iJ-ketoester anions to a (l-phenylthiocyclopropyl)phosphonium cation followed by intramolecular Wittig reaction (J.P, Marino. 1975) produced cyclopentanones. Another procedure starts with a (2 + 21-cycloaddition of dichloroketene to alkenes followed by regioselective ring expansion with diazomethane. The resulting 2,2-dichlorocyclopentanones can be converted to a large variety of cyclopentane derivatives (A.E. Greene. 1979 J.-P. Deprds, 1980). 

Oxindoles can be prepared from Af,p-acylphenylhydrazines by a reaction which is analogous to the Fischer cyclization. This is known as the Brunner reaction. The reaction is typically conducted under strongly basic conditions. For example, heating Af-phenylcyclopentanecarbonylhydrazide with CaO gives a 70% yield of spiro-cyclopentane oxindole[l]. 

At low temperature a 1 1 adduct of thioacetic acid and an enamine could be prepared (709). The previously described reaction of aminomethylene ketones with hydrogen peroxide was extended to bisaminomethylene compounds. However, acylated cyclohexenamines led to cyclopentane-carboxamides (770), Trichloromethyl adducts of enamines and the rearranged amine derivatives were described in a further study (777). 

In addition, the cyclopentylidene ketal has been prepared from dimethoxy-cyclopentane, TsOH, CH3CN, or cyclopentanone (PTSA, CUSO4 >70% yield) and can be cleaved with 2 1 ACOH/H2O, rt, 2 h. Certain epoxides can be converted directly to cyclopentylidene derivatives as illustrated in the following reaction ... 

In the first of these sequences, often called the Torgov-Smith synthesis, the initial step consists in condensation of a 2-alkyl-cyclopentane-l,3-dione with the allyl alcohol obtained from 6-methoxy-l-tetralone and vinylmagnesium chloride. Although this reaction at first sight resembles a classic SN displacement, the reaction is actually carried out with only a trace of base. 

A novel ring closure was discovered by Stork (6) in which the pyrrolidine enamine of a cycloalkanone reacts with acrolein. The scheme illustrates the sequence in the case of 1-pyrrolidino-l-cyclohexene, and the cyclopentane compound was found to undergo the reaction analogously. The procedure details the preparation of the bicyclo adduct and its cleavage to 4-cyclooctenecarboxylic acid. 

Fig. 7-6). Two unichiral amides which have been known capable of this reaction are 1-phenylethylamine [15] and l-(l-naphthyl)ethylamine [16]. Marfey s reagent [N-a-(2,4-dinitro-5-fluorophenyl)-L-alaninamide] was introduced as a reagent to deriva-tize amino acids with cyclopentane, tetrahydroisoquinoline or tetraline structures [17]. Simple chiral alcohols such as 2-octanol can also be used to derivatize acids such as 2-chloro-3-phenylmethoxypropionic acid [18]. 

A general preparation of 2-acetonyl-2,4,6-triaryl-2//-thiopyrans 58 was discovered in the reaction of corresponding 2,4,6-triarylthiopyrylium perchlorates with ethanolic acetone catalyzed with various dialkylammonium salts (86GEP235455, 86JPR573). This preparative procedure was successfully extended to cyclohexane- and cyclopentane- 1,2-diones as the carbonyl components (89JPR853 90GEP280324). The action of bases on thiopyrylium salts may caused their dimerization to thiopyranyl derivatives under suitable conditions (89KGS479). 

A direct application of the ring-opening reaction of an epoxide by a metal enolate amide for the synthesis of a complex molecule can be found in the synthesis of the trisubstituted cyclopentane core of brefeldin A (Scheme 8.35) [68a]. For this purpose, treatment of epoxy amide 137 with excess KH in THF gave a smooth cyclization to amide 138, which was subsequently converted into the natural product. No base/solvent combination that would effect cyclization of the corresponding aldehyde or ester could be found. 

The intramolecular Michael addition of acyclic systems is often hampered by competing reactions, i.e., aldol condensations. With the proper choice of Michael donor and acceptor, the intramolecular addition provides a route to tram-substituted cyclopentanones, and cyclopentane and cyclohexane derivatives. Representative examples are the cyclizations of /3-oxo ester substituted enones and a,/J-unsaturated esters. 

Steady-state kinetics. The cycloaddition reaction between the singlet ground state of 2-isopropylidene cyclopentane-1,3-diyl ( = S ) with acrylonitrile (A) is believed to occur by way of a biradical intermediate (BR),17... 

The reaction of methyl acrylate and acrylonitrile with pentacarbonyl[(iV,iV -di-methylamino)methylene] chromium generates trisubstituted cyclopentanes through a formal [2S+2S+1C] cycloaddition reaction, where two molecules of the olefin and one molecule of the carbene complex have been incorporated into the structure of the cyclopentane [17b] (Scheme 73). The mechanism of this reaction implies a double insertion of two molecules of the olefin into the carbene complex followed by a reductive elimination. 

Table III shows that in the gas phase at a pressure of 40 torr the relative rates of the H2 transfer reactions from the cyclopentane ion to the various additives differ drastically from those derived from liquid phase radiolysis experiments. This indicates that the changes in density may profoundly affect the relative rates of the two competitive reactions, Reactions 22 and 28. Experimental results, which will be described in a later publication, indicate that in the liquid phase an increased importance of the H2 transfer reaction to some of the additives occurs at the expense of the H atom transfer reaction, Reaction 23.

---