Details

Autor(en) / Beteiligte

• Wehrli, Rudolf
• Heimgartner, Heinz
• Schmid, Hans
• Hansen, Hans‐Jürgen

Titel

Thermische (E), (Z)‐Isomerisierungen bei substituierten Propenylbenzolen

Ist Teil von

• Helvetica chimica acta, 1977-09, Vol.60 (6), p.2034-2061

Ort / Verlag

Weinheim: WILEY‐VCH Verlag GmbH

Erscheinungsjahr

1977

Link zum Volltext

Quelle

Alma/SFX Local Collection

Beschreibungen/Notizen

• Thermal (E), (Z)‐Isomerizations of Substituted Propenylbenzenes The thermal isomerizations of (E)‐ and (Z)‐3,5‐dimethyl‐2‐(1′‐propenyl)phenol ((E)‐ and (Z)‐3), (E)‐ and (Z)‐N‐methyl‐2‐(1′‐propenyl)anilin ((E)‐ and (Z)‐4), (E)‐ and (Z)‐3,5‐dimethyl‐2‐(1′‐propenyl)anilin ((E)‐ and (Z)‐5, (E)‐ and (Z)‐2‐(1′‐propenyl)mesitylene ((E)‐ and (Z‐6), (E)‐ and (Z)‐2‐(1′‐propenyl)mesitylene ((E)‐ and (Z)‐7), (E)‐ and (Z)‐2‐(1′‐propenyl)toluene ((E)‐ and (Z)‐8), (E)‐ and (Z)‐4‐(1′‐propenyl)toulene ((E)‐ and (Z)‐9) as well as of (E)‐ and (Z)‐2‐(2′‐butenyl)‐mesitylene ((E)‐ and (Z)‐10) in decane solution were studied (Scheme 2). Whereas the isomerization of the 2‐propenylphenols (E)‐ and (Z)‐3 occurs already between 130 and 150° (cf. Table 1), the isomerization of the 2‐propenylanilins 4 and 5 takes place only at temperatures between 220 and 250° (cf. Tables 2 and 3). The activation values and the experiments using N‐deuterated 4 (cf. Scheme 4) show that 2‐propenylphenols and ‐anilins isomerize via sigmatropic [1,5]‐hydrogen‐shifts. For the isomerization of the methyl‐substituted propenylbenzenes temperatures > 360° are required (cf. Tables 4 and 5). The activation values of the isomerization of (E)‐ and (Z)‐6 and (E)‐ and (Z)‐9 are in accord with those of other (E), (Z)‐isomerizations which occur via vibrationally excited singlet biradicals (cf. Table 7). Nevertheless, thermal isomerization of 2′‐d‐(Z)‐8 (cf. Scheme 6) demonstrates that during the reaction deuterium is partially transfered into the ortho‐methyl group, i.e. 1,5‐hydrogen‐shifts must have participated in isomerization of (E)‐ and (Z)‐8 (cf. Scheme 8). Under the equilibrium conditions 2,4,6‐trimethylindan (17) is formed slowly at 368° from (E)‐ and (Z)‐6, very probably via a radical 1,4‐hydrogen‐shift (cf. Scheme 9). In a similar way 2‐ethyl‐4,6‐dimethylindan (19; cf. Table 6) arises from (E)‐ and (Z)‐7. Thermolysis of (E)‐ and (Z)‐10 in decane solution at 367° results in almost no (E),(Z)‐isomerization. At prolonged heating 19 and 2,5,7‐trimethyl‐1,2,3,4‐tetrahydronaphthalene (20) are formed; these two products arise very likely from an intermolecular radical process (cf. Scheme 10).