Haruo Miyoshi

Oxythallation of norbornene derivatives with thallium(III) acetate in methanol

Abstract Treatment of norbornene, norbornadiene, benzonorbornadiene, and chloro- and methoxy-benzonorbornadiene with thallium(III) acetate in methanol affords only the corresponding cis - exo -acetoxythallation adducts in a sharp contrast to oxymercuration of such strained olefins where methoxymercuration prevails. In the cases of substituted benzonorbornadienes the products are obtained as the regioisomeric mixtures, the isomer ratio being determined by 13 C NMR. In the cases of 5-norbornene-2,3-dicarboxylic anhydride, 5-norbornene-2-methyl-2,3-dicarboxylic anhydride, and 5-norbornen-2- endo -carboxylic acid, lactonization occurs to give a trans -oxythallation adduct having a lactone ring, no introduction of either methoxy or acetoxy groups being observed. 1 H and/or 13 C NMR data for several new oxythallation adducts are provided. The alkaline sodium borohydride reduction of adducts in methanol affords mainly the parent olefin together with 10–16% yields of the corresponding exo -alcohol.

Diacetoxylation of conjugated dienes with thallium(III) acetate in acetic acid

Abstract The reaction of conjugated dienes such as 1,3-butadiene, isoprene, 2,3-dimethyl-1,3-butadiene, 2,5-dimethyl-2,4-hexadiene, 1,3-cyclopentadiene, and 1,3-cyclohexadiene, with thallium(III)acetate in acetic acid at 10–65° for 0.5–15 hr affords an isomeric mixture of the corresponding diacetoxyalkenes (1,2- and 1,4-addition products) in 10–92% yields. The 1,2-addition products are predominantly formed in all cases examined except the case of 1,3-cyclopentadiene. The reaction is assumed to proceed through acetoxythallation and dethallation steps, the latter step being accompanied and/or followed by an attack of acetoxyl group. An initial attack of thallium moiety is proposed to occur mainly at C-1 and C-2 carbons in the cases of linear terminal dienes and cyclic dienes, respectively.

A molecular orbital study of the orienting effect in homoconjugated systems

Abstract Polarization of double bonds in homoconjugated systems has been studied by the use of MO theory and the results obtained have been compared with experimental findings. It has been suggested that the substituent effects are reduced by a structurally determined factor 1 10 ~ 1 100 when they are transmitted through homoconjugation and that the rate of attenuation of the effects would also depend on substituents, being slower in the case of strongly electron-releasing or withdrawing groups and faster in the case of weakly electron-releasing or withdrawing groups. An aspect of polarization in multicyclic conjugated molecules induced by the attacking electrophiles has been discussed in some detail, yielding a fair agreement between the theoretical conclusion and the experimental results accumulated so far.

Acetoxythallation and acetoxymercuration of endo- and exo-dicyclopentadienes and bicyclo[3.2.1] octa-2,6-diene

Abstract Treatment of endo -(I) and exo -dicyclopentadiene (II) with thallium (III) acetate in methanol, chloroform or dichloromethane affords a regioisomeric mixture of the cis-exo -acetoxythallation adducts. The isomer ratios in the adducts were determined directly by 13 C NMR spectra of the crude products. Acetoxymercuration of the same dienes also affords the corresponding regioisomeric cis-exo adducts, the selectivity being lower compared with that of acetoxythallation. Acetoxythallation and acetoxymercuration of bicyclo[3.2.1] octa-2,6-diene (XIII) in dichloromethane gives single cis-exo adducts, respectively.

Acetoxythallation of terminal acetylenes

The reaction of terminal acetylenes with Tl-(OAc)3 in chloroform gives a new type of oxythallation adduct; this was shown to be one of the intermediates in the thallium(III) salt-catalysed conversion of terminal acetylenes into ketones.

Acetoxymercuration of alkylphenylacetylenes

Acetoxymercuration of alkylphenylacetylenes proceeds completely in a trans fashion to give an isomeric mixture of two vinylmercury(II) compounds, the extent of attack of Hg at the carbon α to alkyl group being increased upon increasing the carbon chain length of the alkyl group.

Oxythallation adduct intermediate in hydration of terminal acetylenes by thallium(III) salt catalyst

Reaction of several terminal acetylenes with thallium(III) acetate in chloroform or acetic acid gives a white solid in good yield which is believed to be a new type of oxythallation adduct, (AcO)CR[graphic omitted](OAc)]CR(OAc)(2), on the evidence available to date. From the fact that it is converted into the corresponding ketone and inorganic thallium(III) salt by heating in acetic acid or methanol, it is concluded that it is one of the intermediates in the thallium(III) salt-catalysed conversion of terminal acetylenes into ketones.

Regio- and stereo-selectivity of acetoxymercuration of acetylenes

Acetoxymercuration of alkylphenylacetylenes (PhCCR; R = Me, Et, Prn, or Bun)(1) in acetic acid at 20–60 °C proceeds completely in a trans-fashion to afford a regioisomeric mixture of two vinylmercury(II) compounds, Ph(OAc)CC(HgCl)R (2) and Ph(HgCl)CC(OAc)R (3), the extent of attack of Hg at the carbon a to alkyl group to form (2) being increased upon increasing the carbon chain length ofthe alkyl group [(2)/(3)= 3.0–16.5]. In the case of R = Pri(2) is the sole product, while no acetoxymercuration occurs when R = But. A bridged mercurinium ion intermediate in which phenyl and alkyl groups are bent toward the attacking side of acetate anion is proposed for explaining a marked dependence of the isomer ratio (2) : (3) on the kind of alkyl groups. Similar treatment of diphenylacetylene at 20–95 °C gives only the cis-adduct as reported previously, while that of diethylacetylene affords the trans-adduct and a mixture of trans- and cis-adduct at 20 °C and at 65 °C, respectively. The NaBH4 reduction of (2; R = Me) in neutral condition produces a mixture of (Z)- and (E)-1-acetoxy-1-phenylpropene (ca. 3–5 : 1) in contrast to the reduction of thallium analogue of (2) which gives only the Z-isomer.