Epoxyalkyl propargyl ethers 3a–f and allyl epoxyalkyl ethers 6a–c smoothly undergo radical cyclization reactions using a titanium(III) species (Cp2TiCl) as the radical initiator to form polysubstituted tetrahydropyrans 4a–f and 7a–c in good yields and with high diastreoselectivity. The titanium(III) species was prepared in situ from commercially available titanocene dichloride and Zn dust in THF. On the other
环氧烷基
炔丙基醚 3a-f 和烯丙基环氧烷基醚 6a-c 使用
钛 (III) 物种 (Cp2TiCl) 作为自由基
引发剂顺利进行自由基环化反应,以良好的收率和高非对映选择性形成多取代的
四氢吡喃 4a-f 和 7a-c .
钛 (III) 物质是由市售的
二氯化钛和 Zn 粉尘在 THF 中原位制备的。另一方面,在自由基环化反应中,环氧烷基
炔丙基醚3g和3h分别提供螺
环醚4g和4h作为唯一产物。(© Wiley-
VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)