1,3-dipolar cycloaddition, part 132. Cycloadditions with cyclic seven-membered ketene imines

The cyclic seven-membered ketene imines 8 - isolable despite ring strain - are available by reactions of thiocarbonyl ylides 3 with 2,3-bis(trifluoromethyl)fumaronitrile (4). In contrast to open-chain ketene imines, 8A-8C underwent (2+2) cycloadditions with ethyl vinyl ether at the C=N double bond; the diastereomeric cycloadducts 10 and 11 were characterized by their spectra, and 10A by X-ray analysis. The corresponding adduct 12 from 8A and 2-methoxypropene easily hydrolyzed to give 14. When 8A-8C were treated with diazomethane, (2+3) cycloadditions took place side by side to the C=C and C=N bond of 8. A supposed adduct at the C=C bond, 18A, lost N-2, and 19A was formed which contained a cyclopropylideneamine group; at 50 degrees C, cheletropic elimination produced the isocyanide 22A. Diazomethane addition to the C=N bond of 8 gave rise to condensed 1,2,3-triazoles 21; the HF elimination from the pyrazolines 20 as primary adducts was probably induced by the excess of diazomethane. The structure of 21B was confirmed by X-ray. ((c) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005).