Phenols stereospecific

Ozone hydro gen peroxide Carboxylic acids from phenols Stereospecific ozonolysis... 

Cobalt Oxazoline Palladacycles (COPs) are organocobalt-palladium complexes which catalyse the asymmetric rearrangements of non-chiral allylic trichloroacetamidates with very high enantiomeric selectivity (>90%) to provide chiral allylic amines [it is an aza-Claisen rearrangement, The Overman Rearrangement Overman Carpenter Org React 66 2005, Kirsch, Overman and Watson J Org Chem 69 8101 2004] and in the presence of phenols stereospecific cross-couphng also occurs to provide chiral phenoxyallyl ethers with veiy high (>90%) enantiomeric selectivity [Kirsch, Overman and White Org Lett 9 911 2007, Overman Carpenter Org React 66 2005]. 

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. 

Typically, the stereospecific formation of quaternary centers is as problematic as selective nucleophilic attack at the more substituted carbon of aziridines. Interestingly, a copper mediated methodology has been reported that does both <060L5105>. Although N-tosyl aziridines show favorable results, A-nosyl aziridines gave the best results. The reaction of 89 with a variety of phenols yielded 90 in moderate yields. 

The compounds 43, 45, 48b and 48c gave the corresponding disUoxanes in quantitative yields, and BTSP is converted into hexamethyldisUoxane, 44, formed from difluorote-tramethyldisiloxane. The reaction of 44 with BTSP was not inhibited by 2,4,6-tri(t-butyl)phenol. Compound 48a did not react with di-f-butyl peroxide, which is the carbon analog of BSTP, suggesting an important role of vacant rf-orbitals of the silicon atom. The Si—Si oxidation of compound 49 with BSTP proceeds quantitatively and in a stereospecific fashion (equation 72) . ... 

Where it is possible to distinguish the products, thiol additions show stereospecificity. The products of addition of hydrogen sulfide, thio-phenol, and thiolacetic acid to 1-chlorocyclohexene are to be 75%, 94%, and 66% cis-l, 2-disubstituted cyclohexane, respectively.88 The addition of thiolacetic acid is less stereopecific than the other thiols. The stereospecificity apparently depends upon the ratio of addendum to 1-chlorocyclohexene, Phenylthiyl radical addition to 1-methylcyclo-... 

Decomposition of the species with loss of the apical phenolate presumably would be more rapid than pseudorotation since any such process brings a negatively charged oxygen atom into an apical position. The stereospecific nature of the hydrolysis may also be viewed as arising from the linear steric requirements of nucleophilic displacements on phosphorus and may not involve the actual intermediacy of a pentacovalent species. A large rate enhancement (107) also has been discovered in the oxime-catalyzed hydrolysis of structurally similar phosphonate diester (57) 37. 

An oxidative spiroannulation reaction was carried out for simple phenols and as a result good yields of spiro-compounds containing tetrahydrofuran rings were obtained <02TL3597>. In the stereospecific and enantiospecific total synthesis of the sarpagine indole alkaloid dehydro-16-epinormacusine B, an oxidative cyclization of the alcohol shown below was the key and final step <02OL4681>. 

Conversion of (S)-reticuline to its ( )-epimer is the first committed step in morphinan alkaloid biosynthesis in certain species. 1,2-Dehydroreticuline reductase catalyzes the stereospecific reduction of 1,2-dehydroreticuline to (7 )-reticuline.39 Intramolecular carbon-carbon phenol coupling of (if)-reticuline by the P450-dependent enzyme salutaridine synthase (STS) results in the formation of salutaridine.40 The cytosolic enzyme, salutaridine NADPH 7-oxidoreductase (SOR), found in Papaver bracteatum and P. somniferum, reduces salutaridine to (7S)-salutaridinol.41 Conversion of (7S)-salutaridinol into thebaine requires closure of an oxide bridge between C-4 and C-5 by acetyl coenzyme A salutaridinol-7-0-acetyltransferase (SAT). The enzyme was purified from opium poppy cultures and the corresponding gene recently isolated (Fig.7.2).42,43 In the last steps of morphine... 

The non-phenolic furofuran lignan, (-l-)-eudesmin, from Magnolia kobus var. borealis is formed from pinoresinol by two SAM-dependent methylation steps (Miyauchi and Ozawa, 1998). Cell-free extracts catalysed the successive non-stereospecific methylation both of (-1-)- and (—)-pinoresinol. Thus, the stereospecificity has to be established in an earlier step. 

Fraaije MW, van Berkel WJH. Catalytic mechanism of the oxidative demethylation of 4-(methoxymethyl)phenol by vanillyl-alcohol oxidase. Evidence for formation of a -quinone methide intermediate. J. Biol. Chem. 1997 272 18111-18116. van den Heuvel RHH, Fraaije MW, Ferrer M, Mattevi A, van Berkel WJH. Inversion of stereospecificity of vanillyl-alcohol oxidase. Proc. Natl. Acad. Sci. U.S.A. 2000 97 9455-9460. 

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