Acetates arylvinyl-, reaction with

Shi and coworkers found that vinyl acetates 68 are viable acceptors in addition reactions of alkylarenes 67 catalyzed by 10 mol% FeCl2 in the presence of di-tert-butyl peroxide (Fig. 15) [124]. (S-Branched ketones 69 were isolated in 13-94% yield. The reaction proceeded with best yields when the vinyl acetate 68 was more electron deficient, but both donor- and acceptor-substituted 1-arylvinyl acetates underwent the addition reaction. These reactivity patterns and the observation of dibenzyls as side products support a radical mechanism, which starts with a Fenton process as described in Fig. 14. Hydrogen abstraction from 67 forms a benzylic radical, which stabilizes by addition to 68. SET oxidation of the resulting electron-rich a-acyloxy radical by the oxidized iron species leads to reduced iron catalyst and a carbocation, which stabilizes to 69 by acyl transfer to ferf-butanol. However, a second SET oxidation of the benzylic radical to a benzylic cation prior to addition followed by a polar addition to 68 cannot be excluded completely for the most electron-rich substrates. 

The photochemical reactions of some a-arylvinyl bromides (31), in acetic acid in the presence of sodium acetate and tetraethylammonium bromide (labeled with 8zBr) give nucleophilic substitution, reductive debromination, cis-stilbene photocyclization, and oxidation as the primary pathways to product... 

Photocyclisation to phenanthrenes competes with the photosubstitution reactions of the anisyl substituted arylvinyl bromides (201)however, with the corresponding thioanisyl arylvinyl bromides photosubstitution is the favoured reaction. The products of photosubstitution of (201) are the acetates (202) these also photocyclise to phenanthrenes and no products from fragmentation of the vinyl acetate (as seen for (194) ) were observed. 

G., Photoreactivity of some a-arylvinyl bromides in acetic acid. Selectivity toward bromide versus acetate ions as a mechanistic probe, J. Am. Chem. Soc., 113,4261,1991. See also (b) Kitamura, X, Kabashima, X, Kobayashi, S., and Taniguchi, H., Isolation and alcoholysis of an ipso adduct, vinylidenecyclohexadiene, from photolysis of l-(p-ethoxyphenyl)vinyl bromide. Tetrahedron Lett., 29, 6141, 1988 (c) Kitamura, X, Nakamura, I., Kabashima, X, Kobayashi, S., and Taniguchi, H., A novel spiro adduct from intramolecular ipso substitution in the photolysis of an a-[p-(2-hydroxyalkoxyjphenyl]vinyl bromide,/. Chem. Soc., Chem. Commun., 1154, 1989 (d) Kitamura, X, Kobayashi, S., and Xaniguchi, H., Photolysis of vinyl halides. Reaction of photogenerated vinyl cations with cyanate and thiocyanate ions,/. Org. Chem., 55, 1801, 1990 (e) Hori, K., Kamada,... 

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