Benzene trioxide

While both hydrogenation and epoxidation reactions of (7) (and substituted forms) occur on the oxepin valence tautomer, cycloaddition reactions proceed more readily on the arene oxide form (where the diene is closer to planarity). Thus the dienophiles DM AD and maleic anhydride (MA) readily yielded [4 + 2] cycloadducts with (7) as shown in Scheme 22 (67AG(E)385). A similar type of singlet oxygen cycloaddition reaction gave an unstable endoperoxide (106) which upon heating yielded trans-benzene trioxide quantitatively (equation 14). (75JOC3743). 

The formation of the highly unstable cycloadduct (107) from reaction of (7) with a nitroso compound has been postulated. This intermediate, (107), was proposed to account for the isolation of the frans-dioxazahomobenzene product (78AG(E)936). Intermediate (107) and the final diepoxide product are similar in structure to the endoperoxide (106) and the derived frans-benzene trioxide respectively (equation 15). 

The parent l,4-dihydro-l,4-diazocine (232) and a number of AT,AT-derivatives have been prepared and thoroughly characterized by Prinzbach and Vogel and their colleagues (79AG(E)962, 964, 80CB3161). The benzene diimine precursors have been obtained by two routes. In one case cis benzene dioxide was converted in several steps to the mesyl derivative (225) and thence to the diimine dimesylate. The second proceeds from cis,cis- benzene trioxide to the triimine (227). Two equivalents of acid chloride give the diamides (228) in good yield, and nitrosation with cheletropic elimination of N2O leads to the N,AT -disub-stituted diimines (229). 

Benzene oxide (86), on reaction with singlet oxygen generated either from hypochlorite-hydrogen peroxide or ozone-triphenyl phosphite, forms peroxide 87 in 37% yield. This peroxide on heating in chloroform is quantitatively isomerized to anti-benzene trioxide (42)46 The endoperoxide 88 is similarly... 

An account has also been given of the reaction between benzylmercaptan and cis-benzene trioxide.With a-mercapto esters, p-substituted phenyloxiranes undergo normal opening, without being affected by the substituents on the benzene ring. Chalcone oxides react with mercaptan with accompanying C-C bond cleavage (Eq. 308). ... 

The great variety of transformations that can occur with other sulfur-containing nucleophiles are illustrated by the following experimental observations. Oxiranes react with sulfurated borohydrides in a similar way as the hydrogen sulfide in a basic medium symmetric bis hydroxyethyl disulfides are formed. c/s-benzene trioxide gives di- and triadducts with A, A-diphenylthiocarbamide. Reports have appeared on the reactions between oxirane and -decylmercaptan, butadiene-monooxirane derivatives and mercaptans, and methyloxirane and sulfite ion. ... 

This e c o-peroxide rearranged readily to form the /ra s-benzene trioxide 144 and gave trans-benzene dioxide 142 upon reaction with triphenylphosphite. A similar addition reaction occurred between singlet oxygen and indan 8,9-oxide 7 to yield a further endo-peroxide. An endo-peroxide adduct of an oxepin was also formed when singlet oxygen reacted with 1-benzoxepin 100. Upon deoxygenation with trimethylphosphite, the latter peroxide yielded an aldehyde. ... 

NaOCl (Clorox) and 30% H2 02 reacts with (1) at -5 to -15° to form the endo-peroxide (2) in 37% yield. This substance readily rearranges at 45° to trans-benzene trioxide (3). Singlet oxygen generated from triphenyl phosphite ozonide (3, 323-324) reacts with (1) to form (2), but purification by subUma-tion results in conversion to (3). This trioxide also results from photolysis of (2) (27% yield). 

Benzene dioxide and benzene trioxide are also known [10]. Arene oxides are crucial intermediates in the carcinogenic action of benzo[ z]pyrene and other polycondensed arenes [11]. Oxiranes are found relatively rarely in nature. An example of an oxirane in a natural product is, however, the juvenile hormone of the sphinx moth. 

The possibility of valence isomerization also affects the reactions of the oxepins [5]. For instance, cycloadditions involve the benzene oxide, as shown by the Diels-Alder reaction with activated al-kynes, and give the epoxybicyclo[2.2.2]octatriene 9 or, in the presence of singlet oxygen, afford the peroxide 10. The latter isomerizes thermally yielding the ra .s-benzene trioxide 11 ... 

Epoxide Opening. The lithio propyne derivative (1/2) adds to epoxides in spite of its bulkiness. The TIPS group near the reaction center is useful for preventing secondary reactions in a polyepoxide substrate. Thus while the simple monoadduct (6a) from ds-benzene trioxide and 3-lithio-1-TIPS-1-propyne was formed as a minor product only (always accompanied by products (7a), (8a), (9a), the monoadduct (6b) was isolated in 48% yield (two diastereomers) from the reaction with (1/2) along with 10% (7b) bisadducts (8b/9b) were not formed (eq 6) ... 

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