Fused cyclic compound

In the construction of carbocycles, five-membered ring formation has been used for preparing fused cyclic compounds, such as functionalized diquinanes. ° The reaction of 36 with (TMSlsSiH furnished the expected product 37 in 80% yield and in a or.fi ratio of 82 18, as the result of a kinetic controlled reaction (Reaction 43). 

Triazolopyranopyrimidines can be prepared from the phenol-substituted triazolopyrimidines. Condensation with an aldehyde with the fused dihydropyrimidine such as 181 is followed by cyclization to give benzo-fused trihetero-cyclic compounds 182 (Equation 48) <1996CHE215>. 

The evaluation of the fused cyclic systems as antibacterial compound is by far the most abundant studied biological activity. 

Later Grubbs discovered ruthenium carbene complex and used it for a metathesis reaction to synthesize cyclic compounds 5a-d [Eqs. (6.4) and (6.5)]. In 1995, Grubbs found that ruthenium benzylidene carbene complex Ic," which is now commercially available, has the same reactivity as that of lb. Many researchers have therefore used this complex for olefin metathesis, and this reaction has been useful for the synthesis of carbo- and heterocyclic compounds and fused bicyclic compounds [Eq. [6.6)] °... 

The physical properties of the borepins mentioned above have been compared with those of other seven-membered cyclic compounds. It was concluded that a ring current is present in (56), causing a deshielding of its protons in the NMR spectrum. Benzo and dithieno fused borepins have UV spectra very similar to the correspondingly fused tropones, thus suggesting similar electronic structures. 

The dehydrogenative double silylation method is extended to the synthesis of fused cyclic polycarbosilanes by the condensation of various diynes with l,2,4,5-tetrakis(dimethylsilyl)benzene.62 Polymeric compounds are formed with elimination of H2 [Eq. (20)]. 

The synthesis of five-membered carbo- and hetero-cyclic compounds, including fused rings, has been reported using acetate as a nucleophile in the cyclization of 1,6-enynes under palladium(II) catalysis (Scheme 91). The reaction is initiated by trans-acetoxypalladation of the alkynes and quenched by either trans- or ra-deaceloxypal-ladation in the presence of 2,2/-bipyridine as the ligand.134... 

Several indium-mediated intramolecular carbonyl allylation reactions have been investigated, and it has been found that these reactions provide an easy access to a variety of cyclic compounds. The intramolecular cyclization of 49a-c mediated by indium in aqueous media proceeds smoothly to afford carbocyclic systems containing y-hydroxy-Q -methylene esters 50a-c, which either spontaneously or readily cyclize to give fused o -methylene-y-butyrolactones 51a-c (Scheme 52). The same cyclization of 49d is too slow to compete with the side-reaction, in which the bromide is substituted by a hydroxy group. The ring junction stereochemistry of fused lactones 51 has been found to be cis in all cases. Of the two possible transition states, the one leading to the m-fused compounds is preferred, because the chair-chair conformation is favored over the chair-boat conformation.209... 

One important nitrone is a cyclic compound that has the structure below and adds to dipolarophiles (essentially any alkene ) to give two five-membered rings fused together. The stereochemistry comes from the best approach with the least steric hindrance, as shown. There is no endo rule in these cycloadditions as there is no conjugating group to interact across space at the back of the dipole or dipolarophile. The product shown here is the more stable exo product. 

The Syntex chemists reasoned that, if this methyl ketone could be made stereospecifically by fragmenting a cyclic starting material, the (hard-to-control) double bond stereochemistry would derive directly from the (easier-to-control) relative stereochemistry of the cyclic compound. The starting material they chose was a 5/6-fused system, which fragments to give one of the double bonds. 

Eilbracht et al. by means of rhodium-catalyzed tandem hydroformylation/acetalization of cccw-alkenediols [20]. It had been previously reported that hydroformylation of alkenol resulted in cyclic hemiacetal [21]. Starting from enediols, the authors paved the way for subsequent acetalization, leading to fused bicyclic compounds in a one-pot cascade. As expected, exclusive formation of czs-fused perhydrofuro[2,3fr]furan 6 occurred when applying 60 bar of syngas (CO H2 = 3 1) at 120 °C in dichloromethane to diol 5 in the presence of a [Rh(cod)Cl]2/PPh3 catalytic system (Scheme 4). 

In an attempted synthesis of the spiro compounds 123 from the cyclic 1,1-enediamines 122 derived from cyclic ketones, in contrast to the expectation, the cyclic ketone ring is cleaved under mild reaction conditions and fused heterocyclic compounds 124 are obtained in good yields from 122 and ethyl propiolate (equation 43)58,122. 

Fused pyrazole compounds have been prepared from A -alkyl-substituted pyrazoles. For example, a palladium-catalyzed/norbornene-mediated sequential coupling reaction involving an aromatic sp C-H functionalization as the key step has been described, in which an alkyl-aryl bond and an aryl-heteroaryl bond are formed in one pot. A variety of highly substituted six-membered annulated pyrazoles 433 were synthesized in a one-step process in moderate yields from iV-bromoalkyl pyrazoles 431 and aryl iodides 432 (Equation 87) <20060L2043>. An intramolecular cyclization version has also been reported. Exposure of 2equiv of -butyllithium to l//-pyrazole-l-alkanoic acids 434 afforded the cyclic ketones 435 via a Parham-type cyclization process (Equation 88) <1997SL1013>. 

When phenyl glycine ortho-caxhoxyMc acid is fused with potassium hydroxide it first loses water yielding an acid, indoi llic acid, and this loses carbon dioxide yielding indoxyl. In indoxyl the hydroxyl group is in the 3-position while in the isomeric oxindole it is in the 2-position. All of these comp>ounds are thus condensed hetero-cyclic compounds of a benzene ring and a pyrrole ring. Indole is the mother substance and the others are hydroxy or ketone derivatives. 

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