Five-membered cyclic compounds

AUenic phosphonic acids undergo cyclization reactions in the presence of electrophilic reagents, i.e. proton, bromine (in CHC13) and Hg(OAc)2 (in HOAc), to afford five-membered cyclic compounds [71]. The reaction rate depends greatly on the struc-... 

Carbonyl ylides possess versatile reactivities, among which the 1,3-dipolar cycloaddition is the most common and important reaction. The reaction sequence of ylide formation and then 1,3-dipolar cycloaddition can occur in either inter- or intramolecular manner. When the reaction occurs intermolecularly, the overall reaction is a one-pot three-eomponent process leading to oxygen-containing five-membered cyclic compounds, as demonstrated by the example shown in Scheme 8. A mixture of diazo ester 64, benzaldehyde, and dimethyl maleate, upon heating to reflux in CH2CI2 in the presence of 1 mol% rhodium(ii) perfluorobutyrate [Rh2(pfb)4], yields tetrahedrofuran derivative 65 in 49% yield as single diastereomer. " ... 

Proline, C4H8N—COOH, a-Pyrrolidine Carboxylic Acid This compound is not a simple amino acid but is a carboxyl derivative of a five membered cyclic compound, containing an (—NH—) group, known as pyrrolidine (p. 194 and Part II). 

One of the useful applications of substituted (2-butene-l,4-diyl)magnesium complexes is the facile synthesis of silicon-containing five-membered cyclic compounds. This reaction has been reported earlier for the magnesium complex of 1,3-butadiene [7]. 

Pyrazole A doubly unsaturated five-membered cyclic compound that contains two nitrogen atoms. 

Tetrasulphide A compound that contains four sulphur atoms in a chain, e.g. R-S4 R. Tetrazoline A five-membered cyclic compound that contains four nitrogen atoms and one carbon. 

Allyl radicals were tested as materials or substances that cause cyclization with olefins. 1,5-Hexadiene (diallyl) and diallyl oxalate (DAO) were used as the source materials for allyl radicals. These compounds were subjected to the thermal reaction in the presence of ethylene, which resulted in a rapid formation of five-membered cyclic compounds. The role of allyl radical for the formation of aromatics in pyrolysis reaction is however still... 

The four-membered platinacycle having P=N and Pt=C double bonds 530 undergoes thermal isomerization into a five-membered cyclic compound 531 via orthometallation of the phenyl group of the ligand this complex undergoes addition of P=N bond-containing anions to form the multi-cyclic compound 532 (Scheme 70)." ... 

There are many examples of preparing cyclopentane structures from enynes by gold-catalyzed carbocyclization reactions. Toste et al. have reported that Au(l)-phosphine complexes act as superior catalysts for isomerization of 1,5-enynes to bicyclo[3.1.0]hexenes [124]. For example, treatment of 1,5-enyne (86) with 1 mol% of PhsP-AuPFfi in dichloromethane at room temperature results in formation of cyclopropane-fused cyclopentene (87) in 99% yield (Scheme 18.30). 1,6-Enynes also undergo similar cycloisomerization to five-membered cyclic compounds under the influence of cationic gold(l) catalysts [125, 126], Hydroxylated enynes are versatile precursors for cyclopentenones by gold-catalyzed cycloisomerization... 

Fig. 7.22 The stagnation graph of five-membered cyclic compounds. Clockwise from top left 1,3-cyclopentadiene, p5urole, furan, and thiophene in the presence of a magnetic field perpendicular to the molecular plane. Diamagnetic (paramagnetic) vortices are represented by green (red) lines, and saddle lines are blue. All the stagnation lines lie on the Tcr plane of magnetic synunetry...

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