Cyclopentanes, substituted

In fact, esters of amino alcohols and 2,2-disubstituted plii iiylacetic acids show useful antitussive activity the mecha-lM iii of action may include bronchiodilation. Double alkylation III the anion of phenylacetonitrile with 1,4-dibromobutane gives llit i cyclopentane-substituted derivative (33). Saponification... 

A mixed dimerization to give 20 occurs when the cyclopentane-substituted o -bromoacyl halide 18 is treated with nitrosyltetracarbonyl-chromium (ii), followed by addition of the dialkyl a-bromoacyl halide 19. The yield of the shown mixed dimer is 78... 

Synthetically useful stereoselective reductions have been possible with cyclic carbonyl compounds of rigid conformation. Reduction of substituted cyclohexanone and cyclopentan-one rings by hydrides of moderate activity, e.g. NaBH (J.-L. Luche, 1978), leads to alcohols via hydride addition to the less hindered side of the carbonyl group. Hydrides with bulky substituents 3IQ especially useful for such regio- and stereoselective reductions, e.g. lithium hydrotri-t-butoxyaluminate (C.H. Kuo, 1968) and lithium or potassium tri-sec-butylhydro-borates or hydrotri-sec-isoamylborates (=L-, K-, LS- and KS-Selectrides ) (H.C. Brown, 1972 B C.A. Brown, 1973 S. Krishnamurthy, 1976). 

Substituted cyclopentane lubricants have been commercialized using cyclopentadiene as starting material. These specialty aerospace lubricants have low volatihty and desirable optical properties. 

The term naphthenic acid, as commonly used in the petroleum industry, refers collectively to all of the carboxyUc acids present in cmde oil. Naphthenic acids [1338-24-5] are classified as monobasic carboxyUc acids of the general formula RCOOH, where R represents the naphthene moiety consisting of cyclopentane and cyclohexane derivatives. Naphthenic acids are composed predorninandy of aLkyl-substituted cycloaUphatic carboxyUc acids, with smaller amounts of acycHc aUphatic (paraffinic or fatty) acids. Aromatic, olefinic, hydroxy, and dibasic acids are considered to be minor components. Commercial naphthenic acids also contain varying amounts of unsaponifiable hydrocarbons, phenoHc compounds, sulfur compounds, and water. The complex mixture of acids is derived from straight-mn distillates of petroleum, mosdy from kerosene and diesel fractions (see Petroleum). 

Saturated cyclic hydrocarbons, normally known as naphthenes, are also part of the hydrocarbon constituents of crude oils. Their ratio, however, depends on the crude type. The lower members of naphthenes are cyclopentane, cyclohexane, and their mono-substituted compounds. They are normally present in the light and the heavy naphtha fractions. Cyclohexanes, substituted cyclopentanes, and substituted cyclohexanes are important precursors for aromatic hydrocarbons. 

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. 

In the electrolysis of quinuchdine-2-carboxylic acid decarboxylation occurs without rearrangement (Table 12, No. 5). Stereospecifically substituted cyclopentanes, that... 

Epoxidation of substituted spiro[cyclopentane-l,9 -fluorene]-2-enes 68 with a peroxidic reagent was studied [98], The spiro olefins react with m-chloroperbenzoic acid (mCPBA) in chloroform at 3 °C to give a mixture of the epoxides. In all cases (2-nitro (68b), 4-nitro (68c), 2-fluoro (68d) and 2-methoxyl (68e) groups), the iyn-epoxides, i.e., the syn addition of the peroxidic reagent with respect to the substituent, is favored. For example, for 6 nsyn anti = 63 31 for 68c syn anti = 65 35. Thus, a similar bias is observed in both the reduction of the carbonyl derivatives of 30 and the epoxidation of the derivatives of 68. 

In addition, (Z,Z)-3,4-diethylene-substituted pyrrolidines and cyclopentane are obtained when 2,7-diynes were used as a starting material in Scheme 39. 

An enantioselective variant of the diene cydization reaction has been developed by application of chiral zirconocene derivatives, such as Brintzinger s catalyst (12) [10]. Mori and co-workers demonstrated that substituted dial-lylbenzylamine 25 could be cyclized to pyrrolidines 26 and 27 in a 2 1 ratio using chiral complex 12 in up to 79% yield with up to 95% ee (Eq. 4) [ 17,18]. This reaction was similarly applied to 2-substituted 1,6-dienes, which provided the analogous cyclopentane derivatives in up to 99% ee with similar diastereoselectivities [19]. When cyclic, internal olefins were used, spirocyclic compounds were isolated. The enantioselection in these reactions is thought to derive from either the ate or the transmetallation step. The stereoselectivity of this reaction has been extended to the selective reaction of enantiotopic olefin compounds to form bicyclic products such as 28, in 24% yield and 59% ee after deprotection (Eq. 5) [20]. 

The mechanism for the reaction catalyzed by cationic palladium complexes (Scheme 24) differs from that proposed for early transition metal complexes, as well as from that suggested for the reaction shown in Eq. 17. For this catalyst system, the alkene substrate inserts into a Pd - Si bond a rather than a Pd-H bond [63]. Hydrosilylation of methylpalladium complex 100 then provides methane and palladium silyl species 112 (Scheme 24). Complex 112 coordinates to and inserts into the least substituted olefin regioselectively and irreversibly to provide 113 after coordination of the second alkene. Insertion into the second alkene through a boat-like transition state leads to trans cyclopentane 114, and o-bond metathesis (or oxidative addition/reductive elimination) leads to the observed trans stereochemistry of product 101a with regeneration of 112 [69]. 

Likewise it is possible to differentiate between substituted and unsubstituted alicycles using inclusion formation with 47 and 48 only the unbranched hydrocarbons are accommodated into the crystal lattices of 47 and 48 (e.g. separation of cyclohexane from methylcyclohexane, or of cyclopentane from methylcyclopentane). This holds also for cycloalkenes (cf. cyclohexene/methylcyclohexene), but not for benzene and its derivatives. Yet, in the latter case no arbitrary number of substituents (methyl groups) and nor any position of the attached substituents at the aromatic nucleus is tolerated on inclusion formation with 46, 47, and 48, dependent on the host molecule (Tables 7 and 8). This opens interesting separation procedures for analytical purposes, for instance the distinction between benzene and toluene or in the field of the isomeric xylenes. 

The domino reaction is initiated by the chemoselective attack of the carbanion 2-458 on the terminal ring carbon atom of epoxyhomoallyl tosylate 2-459 to give the alkoxides 2-460 after a 1,4-carbon-oxygen shift of the silyl group. The final step to give the cyclopentane derivates 2-461 is a nucleophilic substitution. In some cases, using the TBS group and primary tosylates, oxetanes are formed as byproducts. 

In a similar way as described for the hydroformylation, the rhodium-catalyzed silaformylation can also be used in a domino process. The elementary step is the formation of an alkenyl-rhodium species by insertion of an alkyne into a Rh-Si bond (silylrhodation), which provides the trigger for a carbocyclization, followed by an insertion of CO. Thus, when Matsuda and coworkers [216] treated a solution of the 1,6-enyne 6/2-87 in benzene with the dimethylphenylsilane under CO pressure (36 kg cm"2) in the presence of catalytic amounts of Rh4(CO)12, the cyclopentane derivative 6/2-88 was obtained in 85 % yield. The procedure is not restricted to the formation of carbocycles rather, heterocycles can also be synthesized using 1,6-enynes as 6/2-89 and 6/2-90 with a heteroatom in the tether (Scheme 6/2.19). Interestingly, 6/2-91 did not lead to the domino product neither could 1,7-enynes be used as substrates, while the Thorpe-Ingold effect (geminal substitution) seems important in achieving good yields. 

To the Buchta heterocycles the higher homologs must also be added. The cyclopentane-1,1,2,2-substituted tetrol 54 was cyclized, in this case heated rapidly with H2S04 at 160-170°, to give the dioxa[3.3.3]propellane 55 in 74 % yield, no dispiran by-product being mentioned here either13). 

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