Oxygen intramolecular

Orendt, A. M., R. Biefofsky, A. B. Pomilio, R. Contreras, and J. C. Facelli. 1991. Ab initio and NMR study of aromatic compounds with dicoordinate oxygenations Intramolecular hydrogen bonding in hydroxy- and methoxybenzene derivatives. J. Phys. Chem. 95 6179-6181. 

The mechanism of the Fries reaction is not known with certainty. One mechanism regards it as a true intramolecular rearrangement in which the acyl group migrates directly from the oxygen atom to the carbon atoms of the ring. Another scheme postulates that the ester is cleaved by the reagent... 

The use of oximes as nucleophiles can be quite perplexing in view of the fact that nitrogen or oxygen may react. Alkylation of hydroxylamines can therefore be a very complex process which is largely dependent on the steric factors associated with the educts. Reproducible and predictable results are obtained in intramolecular reactions between oximes and electrophilic carbon atoms. Amides, halides, nitriles, and ketones have been used as electrophiles, and various heterocycles such as quinazoline N-oxide, benzodiayepines, and isoxazoles have been obtained in excellent yields under appropriate reaction conditions. 

Phenolic oxygen participates in facile oxypalladation. The intramolecular reaction of 2-hydroxychalcone (105) produces the flavone 106[127]. The ben-zofuran 107 is formed from 2-allyIphenol by exo cyclization with Pd(OAc)2, but benzopyran 108 is obtained by endo cyclization with PdChf S], Normal cyclization takes place to form the furan 109 from 2-(l-phenylethenyl)phe-nol[129]. Benzofuran formation by this method has been utilized in the synthesis of aklavinione (110)[130]. 

Although a variety of oxidizing agents are available for this transformation it occurs so readily that thiols are slowly converted to disulfides by the oxygen m the air Dithiols give cyclic disulfides by intramolecular sulfur-sulfur bond formation An example of a cyclic disulfide is the coenzyme a lipoic acid The last step m the laboratory synthesis of a lipoic acid IS an iron(III) catalyzed oxidation of the dithiol shown... 

Next in what amounts to an intramolecular Williamson ether synthesis the alkoxide oxygen attacks the carbon that bears the halide leaving group giving an epoxide As m other nucleophilic substitutions the nucleophile approaches carbon from the side oppo site the bond to the leaving group... 

Intramolecular hydrogen bond between the —OH group and the carbonyl oxygen... 

The chemical structure of a typical divalent metal acetylacetonate, for which the abbreviation would be MCacac). These compounds are internally bonded ionically and complexed to oxygen at the same time. Thus, their intramolecular forces are very strong (they are stable), but their interraolecular forces are weak (they are volatile). 

Propa.ga.tlon, The tertiary THF oxonium ion undergoes propagation by an S. mechanism as a result of a bimolecular colHsion with THF monomer. Only colHsions at the ring a-carbon atoms of the oxonium ion result in chain growth. Depropagation results from an intramolecular nucleophilic attack of the penultimate chain oxygen atom at the exocycHc a-carbon atom of the oxonium ion, followed by expulsion of a monomer molecule. 

The formation of heterocycles derived from quinones is an important synthetic technique. The reaction may be intramolecular, eg, the reaction of (92). Either nitrogen products, eg (93) (yields of 85—91% for R = H, CH, and C H ) or oxygen products (94) are obtained (92,93). Reactions with enamines have been especially important. 

Acyl-, 4-alkoxycarbonyl- and 4-phenylazo-pyrazolin-5-ones present the possibility of a fourth tautomer with an exocyclic double bond and a chelated structure. The molecular structure of (138) has been determined by X-ray crystallography (Table 5). It was shown that the hydroxy group participates in an intramolecular hydrogen bond with the carbonyl oxygen atom of the ethoxycarbonyl group at position 4 (8OCSCII21). On the other hand, the fourth isomer is the most stable in 4-phenylazopyrazolones (139), a chelated phenyl-hydrazone structure. 

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