ABSTRACT

A study of the dienophilic properties of F3CP = C(H)F (1) and F3CP = C (D)F (4) has been performed by using Me3SnP(CF3)CF2H (2) and Me3SnP(CF3)CF2D (3), respectively, as precur­ sors for the in situ generation of 1 and 4 in the presence of 2 ,3-dim ethyl-1,3-butadiene, 1,3-cyclohexadiene or 9,10-dimethylanthracene. Slow elimination of Me3SnF occurs at 55 °C yielding the cycloadducts of 1 and 4, respectively, within 5 or 7 days. Polymerization is observed as the main stabilizing reaction of 1 and 4, thus reducing the yields o f the [2+4]-cycloadducts 5 to 9 to about 20%. They are formed as mixtures o f diastereomers in the ratio a:b ≈ 90:10. In the preferred isomer a according to NMR data CF3 and F have anti positions. Since NMDO calculations yield energy barriers of about 40 kcal/mol for E/Z isomerization, and literature values for inversion barriers of trialkyl phosphanes are of the same magnitude, the formation of isomers most likely has to be explained by a nonconcerted mechanism of the [2 + 4]-cycloaddition.

~ ~~Reactive E =C(p-p)x Systems, XXXIIr1l. -Phosphorus Ylides Me3P = C(X)P(F)CF3 with x-Donor Substituents X = F, OMe, OEtFluorophosphaalkenes of the type F3CP = C(X)F react with tri-of 4 Me3PF2 as main product. The 31P-NMR spectra indicate methylphosphane in a 1: 1 molar ratio at temperatures below a high barrier of rotation for the F,C(F)P group around the -20°C to give the novel phosphorus ylides Me,P= Pr1r-sp2C bond. The new ylides owe their existence to the C(X)P(F)CF, in good yields [X = F (4), 70%; OMe (7), 62%; electron withdrawing effect of the F,C(F)P unit which overOEt (8), 74%) Compounds 4, 7 and 8 are stable up to about compensates the destabilizing influence of the fluorine or l O T , but decompose at higher temperatures yielding in case alkoxy substituents on the sp2C atom.Die stabilen Fluorphosphaalkene F3CP = C(F)NR2 weisen praktisch keinen olefinischen Charakter auf, verfugen stattdessen aber uber ,,amphotere" Eigenschaften. Dies ist dem EinfluD der -1-Substituenten F und CF3 in Kombination mit dem + M-Effekt der NR2-Gruppe zuzuschreiben.So reagiert der Vertreter F3CP = C(F)NMe2

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ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.