Intramolecular rearrangement alcohols

The limited extent of intramolecular rearrangements undergone by the chiral oxonium ions 35 and 36 at 720 torr and at 40 °C (Table 22) allows their use for probing the regio- and stereochemistry of the displacement reactions of Scheme 19. In this case, the allylic alcohol, precursor of the chiral oxonium ions 35 and 36, acts as the nucleophile NuH. The relevant results are condensed in Scheme 21. 

Although the chemistry of pentatetraenylidene complexes [M]=C(=C)3=CR R has not received as much attention as that of aUenylidenes, there is ample experimental evidence to confirm the electrophilic character of the C, Cy and carbons of the cumulenic chain [26-29, 31]. Thus, treatment of tra s-[RuCl(=C=C=C=C=CPh2) (dppe)2][PFg] (132) with alcohols or secondary amines resulted in addition of the nucleophilic solvent across the Cy=Cs double bond to give alkenyl-allenylidenes 138 (Scheme 48) [358]. In chloroform, electrophilic cyclization with one of the Ph groups occurred to give 139. This transformation is actually the parent of the later observed allenylidene to indenylidene intramolecular rearrangement (Scheme 15). 

The reason for the high reactivity lies in the fact that the acid first converts the borane to an acyloxyborane, which then undergoes an intramolecular rearrangement in which the carbonyl group is reduced. Hydrolysis gives the alcohol ... 

H. B. Mereyala and S. Guntha, Stereoselective synthesis of rare (d and l) mono and disaccharides of 5-deoxy hexofuranosiduronic acids by a facile intramolecular rearrangement of hemiacetal heptonolactone alcohols, Tetrahedron, 51 (1995) 1741-1762. 

It is well-known that RuCl(cyclopentadienyl)(PPh3)2 stoichiometrically activates terminal alkynes in the presence of a chloride abstractor to produce [Ru(cyclopen-tadienyl)(=C=CHR)][X] complexes. This reaction has been used with advantage to perform anti-Markovnikov addition of allylic alcohols to terminal alkynes followed by intramolecular rearrangement to produce unsaturated ketones according to Scheme 8 [18, 19]. 

For simple carbonyl compounds, the equilibrium between an aldehyde or a ketone and its corresponding enol is usually so shifted towards the keto form that the amount of enol at equilibrium can neither be measured nor detected by spectroscopy. Nevertheless, as recently emphasised by Hart (1979), this does not mean that the enol cannot exist free, not in equilibrium with ketones and aldehydes. Several examples of kinetically stable enols in the gas phase or in aprotic solvents have been reported. Broadly speaking, it appears that enols have relatively large life-times when they are prepared in proton-free media [e.g. the half-life of acetone enol was reported to be 14 s in acetonitrile (Laroff and Fischer, 1973 Blank et al., 1975) and 200 s in the gas phase (MacMillan et al., 1964)]. These life-times are related to an enhanced intramolecular rearrangement, indicated by the very high energies of activation (85 kcal mol-1 for acetaldehyde-vinyl alcohol tautomerization) which have been calculated (Bouma et al., 1977 Klopman and Andreozzi, 1979) It has therefore been possible to determine most of the spectroscopic properties of simple enols [ H nmr,l3C nmr (CIDNP technique), IR and microwave spectra of vinyl alcohol... 

In addition to the effect pH has on the overall reaction rate, it is also important to note the effect of pH on rearrangement reactions of (+)-catechin. At alkaline pH, these secondary rearrangement reactions dominate. Epimerization of (+)-catechin to (-b)-epicatechin is a prominent reaction at pH 9.0. This is not serious in terms of adhesive formulation because it does not alter the reactivity of the aromatic nucleus toward condensation with benzyl alcohols. However, in reactions at pH 10.0 or 11.0, the intramolecular rearrangement to catechinic acid dominates and results in loss of the phloroglucinol functionality. 

In contrast to the alkene theory the predominant mode of oxidation of the alkyl radicals is by oxygen addition and the alkylperoxy radical so formed then undergoes homogeneous intramolecular rearrangement (reaction (14)). Decomposition of the rearranged radical (reaction (16)) usually leads to a hydroxyl radical and stable products which include O-heterocycles, carbonyl compounds and alcohols with rearranged carbon skeletons relative to the fuel and alkenes. The chain-cycle is then completed by unselective attack on the fuel by the hydroxyl radical (reaction (12)). 

In the 366 A photolysis of nitrobenzene in isopropyl alcohol the quantum yield of disappearance of nitrobenzene is 1.14x 10 the observed products were explained by reactions of triplet state nitrobenzene with the solvent When ortho substituents are present, e.g. aldehyde groups, an intramolecular rearrangement takes place to yield o-nitrosobenzoic acid . The following intermediates have been suggested ... 

The reaction is not limited to self-dimerization, as cyclohexenones also undergo addition to alkenes, acetylenes, and allenes to afford four-membered rings. " However, when the irradiation is carried out in dilute /er -butyl alcohol, bimolecular reactions such as reduction, solvent addition and dimerization are minimized. Under these conditions, it is possible to observe intramolecular rearrangements. 

Corey s group subsequently developed a novel and more efficient conversion of racemic 5-HPETE to racemic LTA4 methyl ester. It was found that allylic hydroperoxides undergo a remarkable intramolecular rearrangement upon treatment with trifluoroacetic anhydride to produce epoxy alcohols in high yields. Standard transformations then effected the conversion of this intermediate to racemic LTA4 methyl ester. 

Grignard reagents readily deprotonate alcohols, secondary amines, and secondary amides in certain substrates, the resulting magnesiated species can undergo inter- or intramolecular addition, or intramolecular rearrangement ... 

That Olah et al. failed to generate the stable ion 520 is attributed by Masamune et al. to the wrong choice of the precursor. According to in alcohol 603, the primary stage is the protonation resulting in an oxonium ion 604 in which the intramolecular rearrangements leading to a methylcyclopentenyl cation proceed faster than the ionization to ion 520. 

It has been noted [390,392,512] that the intermediate allylic hydroperoxide is stereoselectively converted to the cis-epoxy alcohol in the presence of vanadium complexes. Cross-product experiments [390,392], equations (310) and (311), experiments measuring relative rates of epoxidation of cyclohexene and 2-cyclohexene-l-ol [390, 392], effects of added 2other data [390,392] indicate that in the case of vanadium-complex catalyzed oxidation of olefins, epoxy alcohols are formed via intermolecular epoxidation of allylic alcohols rather than by intramolecular rearrangement of allylic hydroperoxides, equation (312). 

The indenylidene-ruthenium complexes were shown to be the actual alkene metathesis catalysts arising from the addition of propargylic alcohols [15-18]. The Dixneuf group [19, 20] later revealed that the intramolecular rearrangement of allenylidene-ruthenium complexes into indenylidene-ruthenium complexes was... 

The homobimetallic, ethylene-ruthenium complex 15, which contains three chloro bridges, was readily obtained from the reaction of [RuCl2(/ -cymene)]2 with 1 atm of ethylene [34]. In 2009, Demonceau and Delaude [34] showed that complex 15 could be a useful precursor to allow subsequent access to the diruthenium vinylidene complex 16, allenylidene complex 17, and indenylidene complex 18 (Scheme 14.8). Upon reaction with propargylic alcohol, complex 15 afforded vinylidene complex 16, which converted into the allenylidene complex 17 in the presence of molecular sieves [34]. As shown in the acid-promoted intramolecular rearrangement of mononuclear ruthenium allenylidene complexes [19, 20, 32], the addition of a stoichiometric amount of TsOH to complex 17 at -50 °C led to the indenylidene binuclear complex 18 [34]. Complex 18 has been well... 

The oxidation of cyclohexanol by concentrated nitric acid is mechanistically complex. A reasonable mechanistic route to the dicarboxyUc acid is given here. The first stage of the oxidation is considered to proceed by a mechanism similar to that found in chromic acid oxidations of alcohols (see Experiment [33]).The reaction here involves the initial formation of a nitrate ester intermediate, which, under the reaction conditions, cleaves by proton abstraction to form the ketone. This reaction is accompanied by reduction of the nitrate to nitrite. The proton transfer may involve a cyclic intramolecular rearrangement during the oxidation-reduction cleavage step. A likely mechanism is outlined below ... 

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