3, 6-Dihydro-2H-selenopyrans 2 with an electron-withdrawing group at the 2-position were prepared by the Diels-Alder reaction of butadienes with selenoaldehydes generated in situ from selenocyanates 1 and triethylamine. Oxidation of the dihydroselenopyrans 2 with 1.5 eq of m-chloroperbenzoic acid provided 2H-selenopyrans 9 and 3, 6-dihydro-2H-selenopyran-2-yl m-chlorobenzoates 10. The benzoates 10 were smoothly converted into the selenopyrans 9 using polyphosphoric acid trimethylsilyl ester. The selenopyrans 9 were methylated with methyl trifluoromethanesulfonate to give Se-methyl selenopyranium trifluoromethanesulfonates 12. Deprotonation of the selenonium salts 12 with sodium hydride or triethylamine generated the selenabenzene derivatives 13, but they were too unstable to be isolated. Therefore, we confirmed the generation of 13 by 1H- and 13C-NMR spectroscopy at -30°C.
丁二烯与由
硒氰酸酯 1 和
三乙胺原位生成的
硒醛发生 Diels-Alder 反应,制备出了在 2 位上带有一个抽电子基团的 3,6-二
氢-2H-
硒并
吡喃 2。用 1.5 eq 间
氯过
苯甲酸氧化二
氢硒并
吡喃 2,可得到 2H-
硒并
吡喃 9 和 3,6-二
氢-2H-
硒并
吡喃-2-基间
氯苯甲酸酯 10。使用多聚
磷酸三
甲基硅酯可将
苯甲酸酯 10 顺利转化为
硒黄檀 9。用三
氟甲磺酸甲酯将
硒基
吡喃 9
甲基化,得到 Se-
甲基硒基吡喃
三氟甲磺酸酯 12。用
氢化
钠或
三乙胺对
硒鎓盐 12 进行去质子化反应,生成了
硒苯衍
生物 13,但它们太不稳定,无法分离出来。因此,我们在 -30°C 温度下通过 1H 和 13C-NMR 光谱确认了 13 的生成。