Palladium-Catalyzed Stereospecific Synthesis of 2,6-Disubstituted Tetrahydropyrans: 1,3-Chirality Transfer by an Intramolecular Oxypalladation Reaction
作者:Nobuyuki Kawai、Jean-Marie Lagrange、Masashi Ohmi、Jun'ichi Uenishi
DOI:10.1021/jo060415o
日期:2006.6.1
(>20:1). Intramolecular cyclizations of the hydroxy nucleophile to the chiral allylic alcohol take place efficiently under mild conditions. A new stereogenic center is generated on the tetrahydropyran ring by 1,3-chirality transfer from the chiral allylic alcohol via a syn-SN2‘ type process. Cis tetrahydropyran 3E was formed from syn-2,8-diols 1a and 2a, and trans tetrahydropyran 4E was formed from anti-2
的PdCl 2(CH 3 CN)2(10摩尔%)壬-3-烯-2,8-二醇的催化反应1和2,得到2,6-二取代的四氢吡喃3和4在具有高非对映选择性优异的产率(> 20: 1)。羟基亲核试剂向手性烯丙基醇的分子内环化在温和条件下有效进行。通过手性烯丙基醇通过syn -SN2'型过程从1,3-手性转移,在四氢吡喃环上生成了一个新的立体异构中心。由顺-2,8-二醇1a和2a形成顺式四氢吡喃3 E,反式四氢吡喃4 E由抗-2,8-二醇1b立体定向形成。顺四氢吡喃轴承顺式烯烃3 ž从获得2b中在-40℃下,而4 ë从形成图2b中的水催化量的存在下,于-40℃。这些环化反应的表面选择性可以通过使中间Pdπ-配合物与烯丙基醇形成良好构象而得以合理化,从而避免了烯丙基应变和1,3-双轴相互作用。立体控制合成光学纯的2-烯基-6-甲基四氢吡喃17从6-甲硅烷氧基-1-庚炔13与醛进行的四个步骤有效地获得了芳基