Phenols, ozonolysis

Investigation of ozonolysis of phenol using y-alumina based catalysts... 

Fig 1 Phenol conversion during ozonolysis with and without y-Al203. 

Complex mixtures of oxidized products are produced in the ozonolysis of BaP on solid substrates. For example, BaP deposited on a glass fiber filter and exposed to 1 ppm 03 in air primarily formed products characteristic of the ring-opening mechanism, e.g., dialdehydes and dicarboxylic and ketocarboxylic acids. However, some quinones and phenols, were also formed. For details on the mechanisms and O-PAH products of these BaP-Ov gas-solid substrate reactions, see Van Cauwenberghe et al. (1979) and Van Cauwenberghe and Van Vaeck (1983 and references therein). 

In order to gain insight into how peroxynitrite attacks activated aromatic substrates, Nonoyama and co-authors (1999) examined the kinetic features of the reaction of peroxynitrite with para-substituted phenols. The authors used ONOONa as a reagent. The latter was prepared by ozonolysis of sodium azide in aqueous solution at pH 12. The reactions... 

Methyldihydrocodeine [xxn] on heating with thionyl chloride is dehydrated to 6-methyldesoxycodeine-C [xxm] phosphorus penta-chloride effects chlorination in position 1 in addition to dehydration. 6-methyldesoxycodeine-C is non-phenolic and gives no formaldehyde on ozonolysis the ozonide on treatment with iodine and alkali yields iodoform, indicating formation of a methyl ketone. Catalytic reduction of [xxm] gives 6-methyltetrahydrodesoxycodeine [xxiv] [16]. 

Acetylphenyldihydrothebaine is formed by acetylation of the phenol [1, 14], Methyl and ethyl ethers of phenyldihydrothebaine were prepared by Freund, who degraded both to nitrogen-free substances [1]. Demethylation of phenyldihydrothebaine affords norphenyldihydro-thebaine [xxxi] which can be methylated to phenyldihydrothebaine methyl ether [1, 4, 8]. The latter is stable to ozonolysis [15]. 

The alkaloids are chiral as a result of restricted rotation of the biaryl system as well as of the possession of asymmetric carbon atoms the methyl at C-3 is on the a-face in all alkaloids and that at C-1 on the B-face in most, but not all cases. The structure of ancistrocladine has been determined by oxidation to the acid (13) the methyl ester of which is prepared by two routes, and by Hofmann degradation of its 0,n-dimethyl-derivative successively to the methine base (14) and the nitrogen-free products (15) and (16), the second of which on ozonolysis gives an aldehyde which yields the lactone (17) on oxidation. The position of the phenolic hydroxyl group in the alkaloid has been confirmed by Claisen rearrangement of the allyl ether (T.R. Govindachari and P.C. Parthasarathy, Tetrahedron, 1971, 1013). 

FIGURE 11.32 Successive ozonolysis of a non phenolic lignin model componnd of the biaryl type. 

Mahanimbine (3a) on ozonolysis " gave the same phenolic aldehyde as had girinimbine, " establishing the common aromatic substitution pattern and D ring type. The remainder of the structure followed from a highly characteristic n.m.r. pattern for the alkenyl-methyl substituted chromene unit. 

A source of the polyketide 9 was the protected equivalent 16 (ref. 13) which can be obtained by ozonolysis of the diene 15 (Scheme 2). Exposure of 16 to silica gel affords phenol 17 which serves as a precursor to a 6,8-dioxygenated isoquinoline. Methylation followed by condensation with ammonia gives isoquinoline 18 from which the isoquinoline 14 can be secured by selective cleavage of the hydroxyethyl group. 

Ozonolysis of diene 19 provides the reduced polyketide 20 which is cyclised to phenol 21 (ref. 13) (Seheme 3). Methylation and a further aldol condensation gives the naphthalene segment 12 while methylation followed by condensation with ammonia yields the C-6 deoxygenated... 

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