Reaction of pyran-2-thiones 4 with nitrosoderivatives led surprisingly to type-8 (19) adducts which proved to be isomeric with the initially expected primary Diels-Alder cycloadducts 5. Methyl 2-thioxo-2H-pyran-5-carboxylate (4f), when reacted with nitrosobenzene at -10°, led quantitatively to the thieto-oxazine intermediate 13, which turned out to be the cornerstone of the complex cycloaddition-rearrangement
吡喃-2-硫酮的反应4与导致令人惊奇的亚硝基衍生物型- 8(19被证明是同分异构体与最初的预期主要)加合物狄尔斯-阿尔德cycloadducts 5。当在-10°下与亚硝基苯反应时,2-thioxo-2 H -pyran-5-羧酸甲酯(4f)定量地导致硫代恶嗪中间体13转化为复杂的环加成重排5 的基石。8个反应途径(方案3)。差示扫描量热法,与18a 19a相同转化,被允许证明该多步重排总体上是高温放热过程,最终产物19代表沿着该反应路径的能量吸收器。
An efficient method for the synthesis of 2,3-dichloro-5-substituted (Cl, CF3, alkyl) pyridines starting from the 1:1 adducts of the copper-catalysed addition of chloral or the corresponding 2,2-dichloroaldehydes to acrylonitrile is presented. Proper choice of experimental conditions allows the preparation of in a one-potprocess. Similarly, the CuCl-catalysed reaction of methyl itaconate with several
the synthesis of 4-methoxycarbonyl-6-trifluoromethyl-2H-pyran-2-one (4) starting from the 1:1-adduct of the CuCl-catalysed addition of 1,1,1-trichloro-2,2,2-trifluoroethane to dimethyl itaconate is presented. The new electrophilic 2-pyrone 4 affords [4+2] cycloadducts with a number of olefins and acetylenes. Their formation follows the reactivity patterns of a typical Diels-Alder reaction with inverse