Optically active phenolic

Finally, there were recently isolated an optically active phenolic compound, dehydrodiconiferyl alcohol (2,3-dihydro-2-(4-hydroxy-3-methoxyphenyl)-5-(3-hydroxypropenyl) - 7-methoxy - 3-benzofuranyl-methanol) (70),192 and a complex 2,3-dihydro-2-phenylbenzofuran, hordanatin A, an antifungal factor 193 it has recently been synthesized,194 and may play a part in the lignification process. 

Recently, Wipf and Ribe reported a novel tandem process in which water accelerates both a sigmatropic Claisen rearrangement catalysed by Erker s catalyst and a subsequent carbometallation reaction with trimethylaluminium providing optically active phenols. Examples of this tandem process are shown in equations 148-150. 

Chiral glyoxylates have been used to effect of/z o-hydroxyalkylation of phenols via coordinative complexes. In this way, optically active 2-hydroxymandehc esters have been obtained with up to 94% diastereoselectivity (36). 

Sulfonic acids are prone to reduction with iodine [7553-56-2] in the presence of triphenylphosphine [603-35-0] to produce the corresponding iodides. This type of reduction is also facile with alkyl sulfonates (16). Aromatic sulfonic acids may also be reduced electrochemicaHy to give the parent arene. However, sulfonic acids, when reduced with iodine and phosphoms [7723-14-0] produce thiols (qv). Amination of sulfonates has also been reported, in which the carbon—sulfur bond is cleaved (17). Ortho-Hthiation of sulfonic acid lithium salts has proven to be a useful technique for organic syntheses, but has Httie commercial importance. Optically active sulfonates have been used in asymmetric syntheses to selectively O-alkylate alcohols and phenols, typically on a laboratory scale. Aromatic sulfonates are cleaved, ie, desulfonated, by uv radiation to give the parent aromatic compound and a coupling product of the aromatic compound, as shown, where Ar represents an aryl group (18). 

The reaction is undoubtedly intramolecular. Evidence for this comes from the absence of crossed-over products when two different ethers were rearranged together121. Further, optically active ortho- 1,3-dimethylallyl phenol is formed from optically active 1,3-dimethylallyl phenyl ether122 and the presence of dienone intermediates has been demonstrated. Claisen and Tietze123 first proposed intermediate dienones such as LXXIX and LXXX. This was established124 when... 

For example /-butyl phenyl ether with aluminium chloride forms para-t-butyl phenol155. Often the de-alkylated phenol is also formed in considerable quantity. The reaction formally resembles the Fries and Claisen rearrangements. Like the Fries rearrangement the question of inter- or intramolecularity has not been settled, although may experiments based on cross-over studies156, the use of optically active ethers157 and comparison with product distribution from Friedel-Crafts alkylation of phenols158 have been carried out with this purpose in view. 

Activated esters for use in peptide-coupling reactions were produced by photolysis of optically active chromium aminocarbenes with alcohols which are good leaving groups, such as phenol, pentafluorophenol, 2,4,5-trichlorophenol, and N-hydroxysuccinimide (Table 17) [ 109]. Since arylcarbenes bearing the op-... 

Allyl p-tolyl sulphoxide 535 reacts with sodium methoxide in methanol by initial prototropic isomerization and subsequent addition of methanol to give 536 (equation 333). Protic solvents are photochemically incorporated by the open chain olefinic bond of trans methyl )S-styryl sulphoxide 537 in a Markovnikov regiospecificity (equation 334). Mercaptanes and thiophenols add to vinyl sulphoxides in a similar manner (compare also Reference 604 and Section IV.B.3) to give fi-alkylthio(arylthio)ethyl sulphoxides 538 (equation 335). Addition of deuteriated thio-phenol (PhSD) to optically active p-tolyl vinyl sulphoxide is accompanied by a low asymmetric a-induction not exceeding 10% (equation 336) . Addition of amines to vinyl sulphoxides proceeds in the same way giving )S-aminoethyl sulphoxides in good to quantitative yields depending on the substituents at the vinyl moiety When optically active p-tolyl vinyl sulphoxides are used in this reaction, diastereoisomeric mixtures are always formed and asymmetric induction at the p- and a-carbon atoms is 80 20 (R = H, R = Me) and 1.8 1 (R = Me, R = H), respectively (equation 337) ... 

On the other hand, it is found that only partial racemization occurs on alkaline hydrolysis of optical active 198 in aqueous methanol136) and no racemization takes place in the hydrolysis of 199 in dioxane/water137). Moreover, the latter reaction is only ca. 80 times faster at 29 °C than that of the analogous morpholide 200, for which a metaphosphorimidate mechanism is precluded a priori by the absence of an NH function and whose hydrolysis is likewise stereospecific,37). Clearly a free metaphosphorimidothioate of type 191 cannot be involved in this case. The experimental findings are compatible, however, with the hypothesis that the nucleophile water attacks a metaphosphorothioimidate/phenolate associate 201. The question of how free metaphosphates occur in solution is of a general nature it has also been considered in the previous Section. 

The synthesis of 3-aryltetrahydroisoquinolines was accomplished by electrophilic aromatic substitution of polysubstituted phenols and phenyl ethers with Lewis acid-generated tosyliminium ions of 2-tosyl-3-methoxytetrahydroisoquinoline derivatives <00SL801>. In addition isoquinoline was reported to react with N-tosylated (R)- or (S)-amino acid fluorides to afford optically active dihydroimidazoisoquinolinones. The reaction proceeds via acylation followed by attack of the tosylamino group at Cl of the intermediate 2-tosylaminoacylisoquinolinium salt <00TL5479>. 

The addition of trimethylsilyl (TMS) cyanide to aldehydes produces TMS-protected cyanohydrins. In a recent investigation a titanium salen-type catalyst has been employed to catalyse trimethylsilylcyanide addition to benzaldehyde at ambient temperature1118]. Several other protocols have been published which also lead to optically active products. One of the more successful has been described by Abiko et al. employing a yttrium complex derived from the chiral 1,3-diketone (41)[119] as the catalyst, while Shibasaki has used BINOL, modified so as to incorporate Lewis base units adjacent to the phenol moieties, as the chiral complexing agent11201. 

Oxidation of phenols and aromatic amines using HRP is generally of little synthetic value, as oligomers and polymers are the main products (5, 260). Under certain conditions oxidative coupling of phenols or naphthols to give biaryls can be achieved, but with low selectivity (262). In contrast, HRP can catalyze a number of useful oxidative N-and 0-deaIkyIation reactions that are relatively difficult to carry out synthetically. This area has been described in detail by Meunier (263). A method for the preparation of optically active hydroperoxides using HRP C has been developed (264). Optically pure (S)-hydroperoxides... 

Me has described the use of an optically active tripodal amine, (25, 65)-2,6-bis(o-hydroxyphenyl)-l-(2-pyridyhnethyl)piperidine (68) as a potent catalyst for methano-lytic ASD of cyclic mei o-anhydrides (Fig. 16) [227], This catalyst was envisaged to adopt a helical conformation thereby providing a highly asymmetric environment for the nucleophihc teri-amine lone pair whilst also allowing activation of the anhydride substrate by the phenolic hydroxyl groups. In the event, ees up to 81% were obtained for the methanolytic ASD of a cyclic meio-anhydride when employed at the 5 mol% level for 20 h at 0 °C in toluene [227]. 

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