No abstract

Xenon difluoride (XeF2) reacts with methanol to form an unstable reactive species CHgOXeF (1). Formaldehyde is produced quantitatively by disproportionation in the absence of unsaturated hydrocarbons or with unreactive alkenes. Hydrogen fluoride generated in situ complexes with 1 to form 2 which reacts with unsaturated hydrocarbons of intermediajte reactivity such as cisor trtms-l-phenylpropene (5c, 5t), indene (6), 2,3-dimethyl-l,3-butadiene (7), and norbornene (8) as an apparent fluorine electrophile and Markovnikov fluoromethoxy products are found.Reaction of XeF2 with methanol in the presence of boron trifluoride as catalyst forms the complex 3 which disproportionates to formaldehyde. Intermediate 3 reacts with unsaturated hydrocarbons of intermediate reactivity (5c, 5t, 6, 7, and 8) as a positive oxygen electrophile to give anti-Markovnikov fluoromethoxy products. However, very reactive (electron rich) alkenes such as dihydropyran ( 9) react rapidly with XeF2 to give a carbocation species before the intermediate 1 (or its complex 2 or 3) can be formed.Recently1® we reported on the methanolysis of xenon

The electrophiles bromine, bromine chloride, chlorine, acetyl hypochlorite, and acetyl hypobromite all yield substantial cis addition product by reaction with indene (1) in aprotic solvents, showing that the direct syn collapse of ion pairs obtained from bromine and similar electrophiles is readily possible. The cis to trans ratios with the halogens (but not with the acyl hypohalites) vary with solvent polarities. In the low-polarity solvents (hydrocarbons and carbon tetrachloride) much more syn addition occurs at high halogen concentration. Syn addition of the above electrophiles to 1 as well as methyl hypobromite and methyl hypochlorite was also observed in methanol and acetic acid, with the exception of bromination in methanol where only the trans-dibromide was obtained.

No abstract

The compositions of dibromide mixtures obtained from the polar bromination of cyclopentadiene, 1,3-cyclohexadiene, and (Z,Z)~, (E,Z)-, and (S,E)-2,4-hexadiene under conditions of kinetic control have been determined. Compositions of equilibrated products were also determined. The stereochemistry of 1,4 addition is found to be primarily cis. The extent of 1,4 addition, which occurs cis, is highest with 1,3-cyclohexadiene and lowest with cyclopentadiene (96 and 52%, respectively, in carbon tetrachloride). The extent of cis 1,4 addition to the 2,4-