(E)-Selective olefination of aldehydes by means of gem-dichromium reagents derived by reduction of gem-diiodoalkanes with chromium(II) chloride
(E)-Selective olefination of aldehydes by means of gem-dichromium reagents derived by reduction of gem-diiodoalkanes with chromium(II) chloride
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DOI：
10.1021/ja00237a081
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发表时间：
1987-02
影响因子：
15
通讯作者：
T. Okazoe;K. Takai;K. Utimoto
中科院分区：
文献类型：
--
作者：
T. Okazoe;K. Takai;K. Utimoto
3醛，因为以下限制：（i）偕双金属化合物的低反应性（Mtl= B5或A16）;（ii）产物缺乏立体选择性;（iii）副反应，例如羰基的还原1或醛还原偶联成1，2-二醇。7最近，Knochel和Normant报道了1-镁1-锌化合物在BF 3-OEt 2的辅助下与醛加成，得到具有良好E选择性的烯烃。8然而，这些试剂限于2-烯丙基取代的1-镁1-锌化合物，因为这些试剂是通过烯基镁化合物的烯丙基锌化制备的。我们在此描述了一种简单和通用的方法，用于通过偕二铬试剂将醛转化为（E）-烯烃，该偕二铬试剂通过在THF中用氯化铬（II）直接还原偕二碘代烷烃13制备，其克服了不稳定的磷叶立德14· 15的弱点（方案II）。表1所示的结果揭示了双生重铬酸盐法的广泛适用性。这一进程的突出特点如下。(1)在所有情况下都观察到高的E选择性，特别是对于脂肪族醛。E/Z比随着醛（R1）上取代基的体积增加而增加。与新戊醛的反应（试验10）是值得注意的，因为即使通过Schlosser的β-氧代叶立德方法也难以从该醛获得E-烷基化产物。15· 16
3 aldehyde because of the following limitations:(i) low reactivity of the geminal dimetallic compounds (Mtl= B5 or Al6);(ii) lack of stereoselectivity of the products; 513· 60 (iii) side reactions such as the reduction of a carbonyl group1 or reductive coupling of an aldehyde to a 1, 2-diol. 7 Recently, Knochel and Normant reported that 1-magnesium1-zinc compounds add to aldehydes with the assistance of BF3-OEt2 to give olefins with good E selectivity. 8 However, the reagents are limited to 2-allyl-substituted 1-mag-nesium 1-zinc compounds, since the reagents are prepared by allylzincation of alkenylmagnesium compounds. We describe herein a simple and general method for the conversion of an aldehyde to an (E)-alkene by means of a geminal dichromium reagent, 9™ 11 prepared by direct reduction of a gem-diiodoalkane13 with chromium (II) chloridein THF, which overcomes the weak points of the nonstabilized phosphorus ylides14· 15 (Scheme II). The results shown in Table I disclose the wide applicabilityof the geminal dichromium procedure. The salient features of the process are as follows.(1) High E selectivity is seen in all cases, especially with aliphatic aldehydes. The E/Z ratios increase with increasing bulkiness of the substituent on the aldehyde (R1). Reaction with pivalaldehyde (run 10) is worth noting, because it is difficult to obtain E-alkylidenation products from this aldehyde even by Schlosser’s/3-oxidoylide method. 15· 16