Tetrahydrofuran Derivatives from Epoxides <i>via</i> Group Transfer Cyclization or Reductive Radical Cyclization of Organotellurium and Organoselenium Intermediates
作者:Lars Engman、Vijay Gupta
DOI:10.1021/jo961578n
日期:1997.1.1
undergo group transfer cyclization to afford 2-substituted 4-[(aryltelluro)methyl]tetrahydrofurans (cis/trans = 1/3-1/10). The aryl beta-(prop-2-ynyloxy)alkyl tellurides similarly afforded 2-substituted 4-[(aryltelluro)methylene]tetrahydrofurans with an E/Z-ratio close to unity. The beta-(allyloxy)alkyl aryl selenides and aryl beta-(prop-2-ynyloxy)alkyl selenides failed to undergo group transfer cyclization
单取代的环氧化物从空间上受阻最小的一面通过苯碲酸根和苯硒酸根试剂进行区域特异性开环,分别得到芳基β-羟烷基碲化物和硒化物。通过在四氢呋喃中用烯丙基溴/氢化钠处理将这些材料进行O-烯丙基化,并在与炔丙基溴/氢化钠反应时将O-prop-2-炔化。在含有40 mol%的六丁基二锡的苯中进行光解后,发现β-(烯丙氧基)烷基芳基碲化物经历了基团转移环化,从而获得了2-取代的4-[((芳基碲基)甲基]四氢呋喃(顺式/反式= 1 / 3- 1/10)。芳基β-(丙-2-炔氧基)烷基碲化物类似地得到E / Z比接近于1的2-取代的4-[(芳基碲基)亚甲基]四氢呋喃。β-(烯丙氧基)烷基芳基硒化物和芳基β-(丙-2-基氧基氧基)烷基硒化物未进行基团转移环化。在氢化三丁基锡和2,2'-偶氮二异丁腈的存在下,发现前一种化合物以高收率进行还原性自由基环化,得到2-取代的4-甲基四氢呋喃(顺式/反式= 1 / 3-1