Cyclopentane synthesis from

Chiral Cyclopentane Synthesis From Sugars Transformation of monosaccharides into enantiomerically pure penta- substituted cyclopentanes via fragmentation and nitrone-olefin dipolar cycloaddition. 

Cyclopentene-l-carboxaldehydes are obtained from cyclohexene precursors by the sequence cyclohexene - cyclohexane-1,2-diol -> open-chain dialdehyde - cyclopentane aldol. The main advantage of this ring contraction procedure is, that the regio-and stereoselectivity of the Diels-Alder synthesis of cyclohexene derivatives can be transferred to cyclopentane synthesis (G. Stork, 1953 G. BUchi, 1968). 

Cyclodimerization of unsymmetrically substituted butatricncs such as 12 give both head-to-head and hcad-to-tail cycloaddition products. The structure of the head-to-head dimer was confirmed by its independent synthesis from the mixed cycloaddition of cumulenes 8 and 10,21 22 These dimerizations proceed by discrete nickel cyclopentanes which was established by the isolation of the 2-bispyridinenickel complex of the l.l,4,4-tetramelhylbuta-l,2,3-triene dimer.23 4-Radialenes with extended conjugation, potential organic conductors and semiconductors, have been prepared by similar methods as illustrated by the examples below.24,25... 

A new stereoselective synthesis of 1,2,3-trisubstituted cyclopentanes based on the Wag-ner-Meerwein rearrangement of a 7-oxabicyclo[2.2.1]heptyl 2-cation starts with the Diels-Alder product of maleic anhydride and a furan (78TL2165, 79TL1691). The cycloadduct was hydrogenated and subjected to methanolysis. The half acid ester (47) was then electrolyzed at 0 °C to generate a cationic intermediate via the abnormal Kolbe reaction (Hofer-Moest reaction). Work-up under the usual conditions provided the 2-oxabicyclo[2.2.1]heptane (48) in 83% yield. Treatment of this compound in turn with perchloric acid effected hydrolysis of the ketal with formation of the trisubstituted cyclopentane (49) in nearly quantitative yield (Scheme 11). Cyclopentanes available from this route constitute useful... 

Oxidation of hydrazo compounds. In an improved synthesis of bicyclo[2.1.03-cyclopentane (6) from the Diels-Alder adduct (1) of cyclopentadiene and diethyl azodicarboxylate (1, 245), Gassman and Mansfield 1 hydrogenated (1) to (2), hydro-... 

That the adsorption of the cyclopentane ring seems to proceed mainly flatly in deuterium exchange on films has been stated above (see Section I,D). Of considerable interest are the investigations on asymmetric catalysis initiated by Schwab et al. (273). In their work, one of the optical isomers reacted a little faster than the other in a racemic mixture. Terent yev and Klabunovskii (274, 273) carried out the catalytic asymmetric synthesis from optically inactive substances. The reactions were accomplished on metals deposited on dextro- and levorotatory quartz. Organic optically active carriers and admixtures give a still greater effect. On this problem see Klabunovskii (276). At the present time still more active catalysts for the reaction of asymmetric hydrogenation and polymerization have been revealed (277-279). 

A 2,5-disubstituted C g tetrahydrofuran fatty ester [13] was obtained from methyl ricinoleate by addition of bromine to the isomerized substrate, followed by hydrogenation over palladium on charcoal (68). Free radical and Lewis acid-induced reactions involving flie double bonds of unsaturated fetty esters have been conducted by Metzger et al. (69-74) these have resulted in the production of a large number of functionalized, cyclic, and branched fetty ester derivatives (e.g., [14], [15]). The synthesis of methyl rac-2-dodecyl-cyclopentane carboxylate from methyl 2-iodo-18 1(6Z) is presented in Scheme 5. 

KondoUf, 1., Eeuerstein, M., Doucet, H. and SanteUi, M. (2007) Synthesis of aU-cw-3-(2-diphenylphosphinoethyl)-l,2,4-tris(diphenylphosphinomethyl)cyclopentane (Ditric )) from dicyclopentadiene. Tetrahedron, 63, 9514-21. 

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. 

RhH(PPh3)4 (1 mol%) exhibited higher catalytic activity and promoted a complete reversal in stereoselectivity to provide the trans isomer of 24 and 25 as the major reaction product. The czs-cyclopentane 29, derived from optically active 28, was converted to the differentially protected cyclopentane triol 29, which, in turn, converted to the differentially protected tetrad 30, a key intermediate in the synthesis of enantiopure bioactive carbo-cyclic nucleosides [19]. 

The synthesis of new 11-deoxyprostaglandin analogs with a cyclopentane fragment in the oo-chain, prostanoid 418, has been accomplished by a reaction sequence involving nitrile oxide generation from the nitromethyl derivative of 2-(oo-carbomethoxyhexyl)-2-cyclopenten-l-one, its 1,3-cycloaddition to cyclopenten-l-one and reductive transformations of these cycloadducts (459). Diastereoisomers of a new prostanoid precursor 419 with a 4,5,6,6a-tetrahydro-3aH-cyclopent[d isoxazole fragment in the oo-chain have been synthesized. Reduction of 419 gives novel 11-deoxyprostanoids with modified a- and oo-chains (460). 

Cycloisomerization represents another approach for the construction of cyclic compounds from acyclic substrates, with iridium complexes functioning as efficient catalysts. The reaction of enynes has been widely studied for example, Chatani et al. reported the transformation of 1,6-enynes into 1-vinylcyclopentenes using [lrCl(CO)3]n (Scheme 11.26) [39]. In contrast, when 1,6-enynes were submitted in the presence of [lrCl(cod)]2 and AcOH, cyclopentanes with two exo-olefin moieties were obtained (Scheme 11.27) [39]. Interestingly, however, when the Ir-DPPF complex was used, the geometry of olefinic moiety in the product was opposite (Scheme 11.28) [17]. The Ir-catalyzed cycloisomerization was efficiently utilized in a tandem reaction along with a Cu(l)-catalyzed three-component coupling, Diels-Alder reaction, and dehydrogenation for the synthesis of polycyclic pyrroles [40]. 

The final chapter in Volume 69 is concerned with the synthesis, stereochemistry, and transformation of cyclopentane-, cyclohexane-, cyclohep-tane-, and cyclooctane-fused 1,3-oxazines, 1,3-thiazines, and pyrimidines and is authored by Professors Ferenc Ftilop, Gabor Bernath, and Kalevi Pihlaja from the Universities of Szeged in Hungary and Turku in Finland. This is a field which has shown rapid development over the last dozen years because of the increased availability of spectroscopic and other analytical methods allowing definition of the precise steric chemistry of these compounds. 

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