Five-membered heterocycle-derived

Eon, C., Pommier, C., and Guiochon, G. Vapor pressures and second virial coefficients of some five-membered heterocyclic derivatives,/. Chem. Eng. Data, 16(4) 408-410, 1971. 

Scheme 23 Five-Membered Heterocycles Derived from 1,2-Amino Alcohols and 1,2-Diamines...

Although the number of Diels-Alder cycloadditions with open-chain and alicyclic dienes is very large, the number of examples with aromatic heterocyclic compounds is relatively small. The introduction of a vinyl group as a substituent onto a heterocycle increases the number of possibilities of reaction. This new possibility, however attractive for synthetic purposes, is successful, with a few exceptions, only with 7r-excessive five-membered heterocyclic derivatives. As is usual in this kind of reaction, Michael additions, ene reactions, [2 + 2]-cycloadditions, and polymerization compete with the Diels-Alder cycloaddition. 

Several structures of selenium and transition metal-containing five-membered heterocycles derived from 1,2,3-selenadiazoles such as complexes 51a, 52, and 53a were determined by X-ray crystallographic analysis <2004POL2967, 2005TL1001, 1999JCD791>. 

Five-membered heterocycles Most papers dealing with the synthesis of cyclic compounds with 10 report on the formation of six-membered or condensed heterocyclic systems. Nevertheless, a number of new five-membered heterocyclic derivatives have been described. So furane, thiophene and pyrrole derivatives were prepared by ring enlargement when oxiranes, thiirane and A -tosylhydrazide, respectively, were reacted with 10 at -10 Various other ways to prepare pyrrole derivatives include cyclization of amino... 

Synthesis of polyfluorinated 1,3-dioxepines has been developed by Burger and coworkers.The method relies on the ring expansion of fluorinated five-membered heterocycles derived from hexafluoroacetone. For example, 4,5-dihydro-... 

As shown in Scheme 2, two heteroatom-carbon bonds are constructed in such a way that one component provides both heteroatoms for the resultant heterocycle. By variation of X and Z entry is readily obtained into thiazoles, oxazoles, imidazoles, etc. and by the use of the appropriate oxidation level in the carbonyl-containing component, further oxidized derivatives of these ring systems result. These processes are analogous to those utilized in the formation of five-membered heterocycles containing one heteroatom, involving cyclocondensation utilizing enols, enamines, etc. 

Unusual heterocyclic systems can be obtained by photodimerizations and for five-membered heterocycles with two or more heteroatoms such dimerizations need be effected on their ring-fused derivatives. Cyclobutanes are usually obtained as in the photodimerization of the s-triazolo[4,3-a]pyridine (540) to the head-to-head dimer (541). These thermally labile photodimers were formed by dimerization of the 5,6-double bond in one molecule with the 7,8-double bond in another (77T1247). Irradiation of the bis( 1,2,4-triazolo[4,3-a]pyridyl)ethane (542) at 300 nm gave the CK0ifused cyclobutane dimer (543). At 254 nm the cage-like structure (544) was formed (77T1253). 

Prototropic tautomerism of isoxazole derivatives has been well studied over a number of years and has recently been reviewed in context with similar behavior in other five-membered heterocycles (70C134, 76AHC(Sl)l, 79AHC(25)147, p. 202). Several generalizations are summarized below. 

The heterocycles have been arranged in the following sequence six-membered rings (aza- and polyaza-benzenes, aza- and polyaza-naphthalenes, etc.) followed by five-membered rings. Derivatives are arranged in alphabetical order according to the substituents. 

Sheremetev and co-workers employed diazo compounds of type 60, prepared from the corresponding amines in moderate yields as alternative excellent precursors for the preparation of side-chain-functionalized derivatives (Scheme 29). Several furazans bearing reactive groups or cyclopropyl or five-membered heterocyclic substituents have been prepared by standard procedures (99MI6). 

Furan and its benzo derivatives 97PF1C117, 98PF1C129, 99PF1C144. Thiophenes, selenophenes, andtellurophenes 97PF1C77,98PF1C87,99PF1C102. Five-membered heterocycles with more than one N atom 97PF1C148,... 

Synthesis of amino derivatives of five-membered heterocycles by Thorpe-Ziegler cyclization 99AHC(72)79. 

The application of spectroscopic methods to the study of tautom-erism proved especially fruitful. The tautomerism of hydroxy and amino derivatives of isoxazole is of great interest to the chemistry of isoxazole this subject, as well as the tautomerism of functional derivatives of other five-membered heterocycles, has been reviewed by Katritzky and Lagowski. We shall therefore only... 

As demonstrated above, nitro derivatives of five-membered heterocycles have found extensive use as antiinfective agents. It is therefore of interest that the nitro derivative of a substituted thiazole was at one time used as an antitrichomonal agent. Bro-mination of 2-aminothiazole (136) (obtained from condensation of thiourea with chloroacetaldehyde) gives the 4-bromo derivative (138) this is then acetylated to 139. Treatment of 139 with nitric acid leads to an interesting displacement of bromine by a nitro group to afford aminitrazole (140)... 

Free amino acids can be derivatized with isothiocyanates to phenyl- or methyl-thiohydantoin derivatives. The thiohydantoins can be separated on a CSP with poly-[Af-acryloyl-L-phenylalanine ethylester] (Chiraspher ) as a chiral selector [25]. This CSP offers a known selectivity for many five-membered heterocyclic rings. 

The 1,3-dipolar cycloadditions are a powerful kind of reaction for the preparation of functionalised five-membered heterocycles [42]. In the field of Fischer carbene complexes, the a,/ -unsaturated derivatives have been scarcely used in cyclo additions with 1,3-dipoles in contrast with other types of cyclo additions [43]. These complexes have low energy LUMOs, due to the electron-acceptor character of the pentacarbonyl metal fragment, and hence, they react with electron-rich dipoles with high energy HOMOs. 

Iwasawa et al. also developed a new reaction involving a three-component coupling process which affords five-membered heterocycles. This [2s+2sh-1c] cycloaddition reaction supposes the consecutive addition of an alkynyllithium derivative to a Fischer carbene complex followed by the addition of a third component which can be an aldehyde, an imine, an isocyanate, or C02 [119] (Scheme 74). 

Hence, microwave irradiation in DMA for 12 min at 120 °C or 30 min at 140 °C, depending on the substrate, resulted in 20 or 21 in 90-96% yields, compared to yields around 50% and a 24 h reaction time for conventional heating. As can be seen in Eq. 2 in Fig. 5, two possibilities exist to connect the heteroaryl bromide part with the five-membered heterocycle (indicated by a and fi. Table 2) that results in a six-membered 2-pyridone ring. Still, a very high selectivity was obtained yielding the 2-pyridones 21, in which the new bond had been introduced at Ca. It should be noted that the obtained structures 20 and 21 represent heterocyclic derivatives of 2-quinolones rather than true 2-quinolones. 

All compounds reported within the review period are indolizines or their hetero-substituted derivatives, fused through the a- or -edge to a five-membered heterocyclic ring. 

Anthranilide derivatives in which an aryl group was directly connected to the anthranilide unit were also reported [63]. Similarly, anthra-nilides connected to a five-membered heterocycle such as thiazole, thiophene, or pyrazole were also covered by the patent literature [64]. Representative examples of these two classes are analogs 16 and 17. 

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