Cyclopenta 5-substituted

A key transformation in Corey s prostaglandin synthesis is a Diels-Alder reaction between a 5-(alkoxymethyl)-l,3-cyclopenta-diene and a ketene equivalent such as 2-chloroacrylonitrile (16). As we have already witnessed in Scheme 3, it is possible to bring about a smooth [4+2] cycloaddition reaction between 5-substituted cyclopentadiene 15 and 2-chloroacrylonitrile (16) to give racemic 14 as a mixture of epimeric chloronitriles. Under these conditions, the diastereomeric chloronitriles are both produced in racemic form because one enantiotopic face of dienophile 16 will participate in a Diels-Alder reaction with the same facility as the other enantiotopic face. In subsequent work, Corey s group demonstrated that racemic hydroxy acid 11, derived in three steps from racemic 14 (see Scheme 3), could be resolved in a classical fashion with (+)-ephe-... 

Studies of chlorination and bromination of 2//-cyclopenta[reactivity differences dependent on substituents and halogenation conditions. In monochlorination the unsubstituted compound was more reactive than its 2-methyl and 2-phenyl derivatives, the reactivity ratio being 7.1 1.7 1 [78H(11)155]. Chlorination occurred most readily in the 5- and 7-positions of the cyclopentadienyl moiety, but once all three positions had been substituted, NCS attacked the methyl group... 

Irradiation of the potassium salt of the substituted cyclopenta[b]pyrrole-2-carboxylic acid 389 results in formation of the central piperazine core of 390 following decarboxylation (Equation 104) <20010L537, 2003JA10664>. 

A Nazarov-type cyclization was exploited to prepare annelated pyrroles <06OL163>. Acylation of iV-tosylpyrrole 65 with carboxylic acid 66 promoted by trifluoroacetic anhydride gave intermediate 2-ketopyrrole 67 which underwent a Nazarov-type cyclization to give cyclopenta[fc> pyrrolc 68. Another route to cyclopenta[fc]pyrroles involved a novel cyclization involving pyrrole-substituted enones and isocyanides <06OL3975>. 

Starting from 1-substituted-16-(12/f-l l-oxa-17-thia-15-aza-cyclopenta[ ]phenathrene-16-yl)-hydrazines, the reaction with formic acid or acetic anhydride gave novel l-substituted-6//-5-oxa-7-thia-8,9,10a-triaza-pentaleno[4,5- ]-phenathrenes, and l-substituted-10-methyl-6/7-5-oxa-7-thia-8,9,10a-triaza-pentaleno[4,5- ]phenathrenes, whose in vitro antibacterial activity has been also evaluated 111 NMR and MS data are described <2006EJM891>. 

The other necessary reaction for a BN to VN isomerization is a well precedented 1,5 H shift to convert the linearly conjugated substituted cyclopentadiene (LCC) into the cross conjugated cyclopenta-diene (CCC). The relative lability of BN relative to VN is thus a reflection of the stabilizing conjugation of the substituent in the vinyl isomers and the fact that the formation of LCC from BN is more favorable than the formation of CCC from the retro Diels Alder of VN. The relative energetics for all of these processes is represented in a combined reaction profile diagram shown in Figure 1. 

Hill, C.L., Verma, C.S. and Grogan, G., Des3mimetrisations of l-alkylbicyclo[3.3.0]octane-2,8-diones by enzymatic retro-Claisen reaction yield optically enriched 2,3-substituted cyclopenta-nones. Adv. Synth. Catal. 2007, 349, 916. 

A review of Diels-Alder reactions of fullerenes with acyclic and cyclic dienes has been presented. The addition of substituted pyrimidine o-quinodimethanes (75) to [60]fullerenes yields novel organofullerenes (76) bearing a pyrimidine nucleus covalently attached to the Ceo cage (Scheme 26). The Diels-Alder dimerization of cyclopenta[/]phenanthrene (77) with isobenzindene (78) yields the dimer (79) in 85% yield (Scheme 27). Further evidence has been supplied to support an early reorganization of the r-network in the dimerization of 2-methoxycarbonylbuta-1,3-diene. The Lewis acid-catalysed Diels-Alder reactions of acrylate derivatives of new carbohydrate-based chiral auxiliaries with cyclohexadiene show excellent endo. exo... 

When l-[o-(phenylethynyl)phenyl]cyclopropanol-Co2(CO)6 complex (36) is heated at 50 °C in 2-propanol under argon in the presence of DABCO, a completely different product, 3a,4-dihydro-3ff-cyclopenta[a]inden-2-one derivative 40, is produced as a 95 5 diastereomeric mixture in 72% yield. As shown in Scheme 18, not only aryl-substituted alkynyl derivatives, but also alkyl-substituted alkynyl derivatives, give the corresponding cyclopenta[a]inden-2-one derivatives 40 in moderate to good yields. 

Cyclopenta-l,2,3-dithiazole 140 was formed through a reaction of 2-substituted cyclopentanone oximes and S2CI2 (Scheme 71 2001CC403). Exhaustive chlorination accompanied this reaction as in the case of other cyclopentadithioles (see above). 

The ring system can be generated by Diels-Alder addition of a substituted cyclopenta-dienone and an alkyne. A reaction sequence involving addition followed by CO elimination can be used for the synthesis of highly substituted benzene rings.217 218 219... 

The ansa metallocene initiators are synthesized in a relatively straightforward manner (Eq. 8-53). Cyclopentadiene or a substituted analog such as an alkyl-substituted cyclopenta-diene, indene, 4,5,6,7-tetrahydroindene, or fluorene (CpH2) is reacted with butyllithium to... 

Diels-Alder adducts of 1-substituted cyclopentadienes could also be obtained through a one-pot procedure whereby ethyl acrylate is initially employed to consume aU 2-substituted cyclopentadienes. Subsequently, various 2,5-disubsti-tuted benzoquinones are added to react with remaining 1-substituted cyclopenta-... 

Steroids are compounds possessing the tetracyclic skeleton of cyclopenta[a]phenan-threne (1) or a skeleton derived therefrom by one or more bond scissions or ring expansions or contractions. Natural steroids have trivial names. The nomenclature of steroids is not based on these trivial names, but on a few stereoparent hydrides that are common to many compounds. Substitutive nomenclature is used to designate characteristic groups and unsaturation. Structural modifications are expressed by appropriate non-detachable prefixes. 

Chlorinated cyclopenta-l,2,3-dithiazoles such as (105) and (125) (Section 4.11.8.5) are susceptible to nucleophilic substitution (e.g. Equation (13a))) <93JCS(P1)769>, whereas chlorinated cyclohepta-1,2,3-dithiazoles of the type (127)-(129) (Section 4.11.8.5) do not react with nucleophiles. This difference may be explained by the opposite charge separation between fused cycles in the two... 

There are a number of examples of the synthesis of chromans using o-quinone methides as the heterodiene in a hDA reaction. Both pyrano[3 -c]-benzopyrans and cyclopenta[c][l]benzopyrans result from an intramolecular cycloaddition of a substituted o-quinonemethide generated under mild conditions. In the former case, salicylaldehyde and an unsaturated alcohol yield the rra/is-fused tetrahydropyranobenzopyran (Scheme 10) <99JOC9507>. However, the latter synthesis (Scheme 11) is less selective <99BCJ73>. 

Goldring, J. M., L. M. Ball, R. Sangaiah, and A. Gold, Synthesis and Biological Activity of Nitro-Substituted Cyclopenta-Fused PAH," in Polynuclear Aromatic Hydrocarbons A Decade of Progress (M. Cooke and A. J. Dennis, Eds.), pp. 285-299, Battelle Press, Columbus, OH, 1988. 

Organosilyl substituted 7)5-cyclopentadienyl complexes may be prepared by two main procedures (a) reactions of silylated cyclopenta-dienes or their alkali metal derivatives, with an appropriate transition metal compound (carbonyl or halide) with formation of ir-bonds (b) metalation of a preformed 7j5-cyclopentadienyl complex, followed by treatment with an organohalosilane. 

Treatment of bis(dimethylaminomethylene)pyrrolizinium perchlorate (29) with cyclopentadiene-NaH in DMF gave the diatropic cyclopenta-[fc]cycl[4,2,2]azine (77), which was also obtained from the fulvene derivative (78) and 3//-pyrrolizine (25). Electrophilic substitutions (deuteration, nitration, nitrosation, acylation, bromination, Mannich reaction) occur in the 6- and 8-positions.32... 

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