Cyclopentanes, alkyl-substituted—

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). 

Alkylphosphanes, chelating, 42 482 Alkyl-substituted cyclopentanes, aromatization. 

The first vinyllithium carbolithiation reaction was reported by Chamberlin and Bloom15, who showed that vinyllithium reagents derived from ketone trisylhydrazones undergo anionic cyclization reactions to give functionalized cyclopentanes (Scheme 4). These authors have also shown that 5-, 4- and 3-alkyl-substituted 2-lithio-l,6-heptadienes like... 

Substitution at the 2-position of the allylic system is incompatible with the process and only open-chain products are observed under the standard reaction conditions. However, an impressive example of the stereocontrolled synthesis of a cyclopentane ring substituted at each position results from the combination of donor and acceptor components, both of which are alkyl substituted. 

The greater lability toward vanadium removal and porphyrin destruction for the vanadyl petroporphyrins over the synthetic vanadyl porphyrins is a fortunate circumstance. This difference can be rationalized based upon structural differences of the porphyrins involved. Phyllo-type petroporphyrins all contain a cyclopentane ring, fused to one of the pyrrole rings with the methine carbon one of the units of the carbo-cyclic structure. Etio- and rhodo-type petroporphyrins appear to have alkyl substitution at one or more methine positions, as based upon nmr spectral data. Should all petroporphyrins have a carbon substituent on one or more methine carbons, the carbonium ion formed by the reaction would tend to have more charge localization on those methine carbons. These ions are a more stable species by an order of magnitude over those porphyrins without methine substitution. 

With various alkyl-substituted cyclopentanes, ring-opening selectivity with Ir/A Os depended on the number of CH2—CH2 bonds, which argues for the dicarbene mechanism, in which the intermediate is a l,l,2,2-a4 species. The chemisorbed state of cyclopentene was reported to be more or less perpendicular to the Ir(l 11) surface by a NEXAFS study, in support of this mechanism. 

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... 

The reactivity of allyl radicals does, however, appear to be sufficient for intramolecular radical reactions. In a systematic study, Stork and Reynolds investigated the feasibility of allyl radical 5-exo cyclizations41. It was found that cyclization proceeds readily for a variety of systems, especially for those with geminal 3,3-diester substitution. Mixtures of c/s/fraws-cyclopentanes are formed as the major products, while 6-enclo cyclization is hardly observed42. Allyl radicals behave in this respect much like alkyl radicals43. Cyclization is not even hindered by the presence of substituents at the attacked carbon... 

Similar to Rueping s procedure, Hua and coworkers developed a BiCl3-catalyzed synthesis of 1,1-diarylalkanes also starting from electron-rich arenes and styrenes [68]. They found that styrenes 37 could be transformed to the substituted cyclopentanes 39 if catalytic amounts BiCl3 were applied (Scheme 30). This reaction is believed to proceed via an intermolecular ene-reaction between styrene and the carbocationic intermediate I, followed by an intramolecular Friedel-Crafts alkylation of the resulting intermediate II. 

Shibata and co-workers have reported an effective protocol for the cyclization/hydrosilylation of functionalized eneallenes catalyzed by mononuclear rhodium carbonyl complexes.For example, reaction of tosylamide 13 (X = NTs, R = Me) with triethoxysilane catalyzed by Rh(acac)(GO)2 in toluene at 60 °G gave protected pyrrolidine 14 in 82% yield with >20 1 diastereoselectivity and with exclusive delivery of the silane to the G=G bond of the eneallene (Equation (10)). Whereas trimethoxysilane gave results comparable to those obtained with triethoxysilane, employment of dimethylphenylsilane or a trialkylsilane led to significantly diminished yields of 14. Although effective rhodium-catalyzed cyclization/hydrosilylation was restricted to eneallenes that possessed terminal disubstitution of the allene moiety, the protocol tolerated both alkyl and aryl substitution on the terminal alkyne carbon atom and was applicable to the synthesis of cyclopentanes, pyrrolidines, and tetrahydrofurans (Equation (10)). 

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