Heterocyclic compounds rearrangement

Photochemical fragmentation Equilibria with open-chain compounds Rearrangement to other heterocyclic species Polymerization... 

Plant growth regulators heterocyclic compounds as, 1, 191 Platinacyclobutane, dichloro-, 1, 666 Platinacyclobutanes reactions, 1, 667 rearrangement, 1, 667 synthesis, 1, 672 Platinacyclobutenones synthesis, 1, 666 Platinacycloheptanes synthesis, 1, 672 Platinacyclohexanes synthesis, 1, 672 Platinacyclopentanes synthesis, 1, 672... 

In this review an attempt is made to discuss all the important interactions of highly reactive divalent carbon derivatives (carbenes, methylenes) and heterocyclic compounds and the accompanying molecular rearrangements. The most widely studied reactions have been those of dihalocarbenes, particularly dichlorocarbene, and the a-ketocarbenes obtained by photolytic or copper-catalyzed decomposition of diazo compounds such as diazoacetic ester or diazoacetone. The reactions of diazomethane with heterocyclic compounds have already been reviewed in this series. ... 

The simple ring opening of tetrahydro-1,3-oxazine derivatives is not the only possible reaction of these heterocyclic compounds catalyzed by mineral acids. An interesting rearrangement of 6-aryl-6-alkyltetrahydro-l,3-oxazines when warmed with concentrated hydrochloric acid was found by Schmiedle and Mansfield ... 

O- and N-containing heterocyclic compounds Characteristic rearrangement ion of butyrates except methyl Dinitrotoluenes Trimethylsilyl derivatives... 

Benzoxazines are heterocyclic compounds obtained from reaction of phenols, primary amines, and formaldehyde.98,99 As described previously, they are key reaction intermediates in the HMTA-novolac cure reaction.40,43 Crosslinking benzoxazine monomers at high temperatures gives rise to void-free networks with high Tgs, excellent heat resistance, good flame retardance, and low smoke toxicity.100 As in HMTA-cured novolac networks, further structural rearrangement may occur at higher temperatures. 

Dipolar cycloaddition reactions of thioisoraunchnones (l,3-thiazolium-4-olates) have not been as extensively studied as those of munchnones (l,3-oxazolium-5-olates) despite offering rapid access to novel heterocyclic compounds. The cycloaddition of the thioisomunchnone (52) with trans-P-nitrostyrene results in the formation of two diastereoisomeric 4,5-dihydrothiophenes (53) and (54) via transient cycloadducts. These cycloadducts then undergo rearrangement under the reaction conditions <96JOC3738>. 

Strecker aldehyde are generated by rearrangement, decarboxylation and hydrolysis. Thus the Strecker degradation is the oxidative de-amination and de-carboxylation of an a-amino acid in the presence of a dicarbonyl compound. An aldehyde with one fewer carbon atoms than the original amino acid is produced. The other class of product is an a-aminoketone. These are important as they are intermediates in the formation of heterocyclic compounds such as pyrazines, oxazoles and thiazoles, which are important in flavours. 

The central Co,=Cp double bond of an allenylidene backbone can also react with a variety of dipolar organic substrates to yield cyclic adducts. Most of the cychza-tion processes reported occur in a stepwise manner via an initial nucleophilic attack at the Coi atom and further rearrangement of the molecule involving a coupling with the Cp carbon. Representative examples are the reactions of the electron-poor ruthenium-allenylidene complex 46 with ethyl diazoacetate and 1,1-diethylpropar-gylamine to yield the five- and six-membered heterocyclic compounds 82 and 83, respectively (Scheme 29) [260, 284]. 

Photochemical rearrangement has been reported for heterocyclic compounds, as shown in the esters of hydroxypyridine [79-81]. An example is shown... 

Oxidative rearrangements resulting in the formation of heterocyclic compounds are relatively less explored, although some of them are quite important. A basic reaction is the conversion of a chalcone to 3,3-dimethoxy-l-phenylpropanone (Eq. 2) (85TL2961). This process may be adapted to heterocyclic synthesis. 

The most frequent rearrangement of substituted hydroxylamines is the thermal [3,3]-sigmatropic rearrangement, the 3-aza-4-oxa-Cope rearrangement also called 3-aza-4-oxy-Cope rearrangement, that proceeds by a cyclic six-membered transition state (equation 1). Albeit the difficulty to prepare hydroxylamine derivatives, this rearrangement proceeds in mild conditions and is useful in the synthesis of several heterocyclic compounds. 

The same strategy had application in several other heterocyclic compounds, to obtain either amine or carboxylic acid derivatives. A process for the production of 4-amino-5-methylpyrazole derivative 325 using the Beckmann rearrangement as a key step was the subject of a new patent ° (equation 119). 

Much work has been devoted to [2 + 3] cycloadditions both in the synthesis of and in reactions of this kind of heterocycle. Dimroth rearrangement is another feature which has been explored widely. X-ray structural analysis was extensively used alongside physico-chemical methods to elucidate the structure of novel compounds. 

The rearrangement also occurs with analogous heterocyclic compounds. 3,4-Dihydro-2//-pyrans are photoisomerized to produce cyclobutanecarbaldehydes. Thus, 3,4-dihydro-2//-pyran (5) is refluxed in the presence of mercury and irradiated with light from a quartz tube with a wavelength of 254 nm to give cyclobutanecarbaldchyde (6).88... 

Photolysis of acid azides, yielding AT-heterocyclic compounds, has been reported, e.g., the formation of benzoxazolone (CCXXXIX) via the photolysis of salicyclic acid azide (CCXXXVIII). It is suggested that the photolysis of benzoylazide (CCXL) proceeds via the intermediate radical (CCXLI) which rearranges to phenyl isocyanate (CCXLII). 

A. Padwa, in P. de Mayo (ed.). Rearrangements m Ground and Excited States, vol. 3, Academic Press (1980). This review looks at the photochemical rearrangements of heterocyclic compounds with a five-membered ring. 

Because carbenes and nitrenes give several modifications of heterocyclic compounds,253 other reactions are likely to be reported under phase transfer conditions. Of special interest are rearrangements following addition of carbenes to heterocyclic molecules. 

N—N Bond Cleavage and Rearrangements of Arylhydrazones and Arylhydrazides — Recent Developments R. Fusco and F. Sannicolo, Tetrahedron, 1980, 36, 161-170. An Application of Beta-Lactam to the Synthesis of Heterocyclic Compounds S. Kano, Yuki Gosei Kagaku Kyokaishi, 1978, 36, 581-594. 

Thio-Claisen Rearrangement in the Synthesis of Sulfur-containing Heterocyclic Compounds A. V. Anisimov and E. A. Viktorova, Khim. Geterotsikl. Soedin., 1980, 435-449. 

Conidine — see 1-Azabicy,clo[4.2.0]octane Conjugation reactions nitrogen heterocycles at carbon, 1, 239 at nitrogen, 1, 234-238 Conjunction nomenclature, 1, 37 Contagious bovine pleuropneumonia heterocyclic compounds as, i, 205 A Convention nomenclature, 1, 32 Con vi cine occurrence, 3, 144 Cook-Heilbron s synthesis thiazoles, 6, 300-301 Cope rearrangement, 7, 35 Copper... 

Monocyclic and fused 1,3,5- and 1,3,6-oxadiazepines are accessible either by one-component cyclization (see Scheme 22), [1+6] cyclocondensation, [3+4] condensation (substitution) reaction, heterocyclic ring rearrangement (see also CHEC(1984) and CHEC-II(1996)), or multicomponent reactions (Scheme 37). The 1,3,5-oxadiazepine heterocyclic ring is also present in iminonucleosides, such as compounds 142 (Scheme 29), which are available via one-component cyclization and [1+6] cyclocondensation reactions. 

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