ASYMMETRIC-SYNTHESIS USING DIISOPROPYL TARTRATE MODIFIED (E)-CROTYLBORONATES AND (Z)-CROTYLBORONATES - PREPARATION OF THE CHIRAL CROTYLBORONATES AND REACTIONS WITH ACHIRAL ALDEHYDES
ASYMMETRIC-SYNTHESIS USING DIISOPROPYL TARTRATE MODIFIED (E)-CROTYLBORONATES AND (Z)-CROTYLBORONATES - PREPARATION OF THE CHIRAL CROTYLBORONATES AND REACTIONS WITH ACHIRAL ALDEHYDES
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DOI：
10.1021/ja00173a023
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发表时间：
1990-08-15
影响因子：
15
通讯作者：
HALTERMAN, RL
中科院分区：
文献类型：
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作者：
ROUSH, WR;ANDO, K;HALTERMAN, RL
酒石酸二异丙酯改性的（E）-和（Z）-巴豆基硼酸酯2和3容易制备，具有非常高的异构体纯度（≥ 100%）。98% E（2）; ≥99%Z代表3），通过在THF中用n-Buli和KOtBu金属化（E）-和（Z）-2-丁烯，然后用（i-PrO）3-B处理（E）-和（Z）-丁烯基钾4和5，水解，并与酒石酸二异丙酯（DIPT）酯化。（E）-巴豆基硼酸酯2已经以400-mmol规模制备，具有优异的结果。还描述了2和3的溶液的制备和标准化的程序。巴豆基硼酸酯2和3与脂族（直链或α-链）化合物进行高度非对映和对映选择性反应。单支化的; 72- 91%ee），芳香族和α，.贝塔不饱和醛（55- 74%ee）。反应的非对映选择性与试剂异构体纯度密切相关，特别是对于在-78 ℃下进行的反应。C.对映选择性是最好的甲苯中的所有基板，除了苯甲醛，其中最好的结果是在THF中获得。通过与Sharpless不对称环氧化反应制备的环氧醇的相关性，对本研究中合成的14种均烯丙基醇中的9种进行了相对和绝对立体化学归属。在每种情况下的结果与优先通过过渡态A进行的不对称巴豆基硼化反应一致。也就是说，假定RCHO的R优先于转移的巴豆基，则（R，R）-2和（R，R）-3总是产生在甲醇中心具有S构型的高烯丙基醇。由（S，S）-DIPT制备的试剂（S，S）-2和（S，S）-3可简单地得到高烯丙醇的对映体组。
Diisopropyl tartate modified (E)- and (Z)-crotylboronates 2 and 3 are easily prepared with very high isomeric purity (.gtoreq. 98% E for 2; .gtoreq. 99% Z for 3) via the metalation of (E)- and (Z)-2-butene with n-Buli and KOtBu in THF followed by treatment of the (E)- and (Z)-crotylpotassiums 4 and 5 with (i-PrO)3-B, aqueous hydrolysis, and esterification with diisopropyl tartrate (DIPT). (E)-Crotylboronate 2 has been prepared on 400-mmol scales with excellent results. A procedure for the preparation and standardization of solutions of 2 and 3 is also described. Crotylboronates 2 and 3 undergo highly diastereo- and enantioselective reactions with aliphatic (linear or .alpha.-monobranched; 72-91% ee), aromatic and .alpha.,.beta.-unsaturated aldehydes (55-74% ee). The reaction diastereoselectivity closely parallels the reagent isomeric purity especially for reactions performed at -78.degree. C. The enantioselectivity is best in toluene for all substrates except benzaldehyde where best results are obtained in THF. The relative and absolute stereochemistry of 9 of the 14 homallyl alcohols synthesized in this study were assigned by correlation with epoxyalcohols prepared by the Sharpless asymmetric epoxidation. The results in each case are consistent with the asymmetric crotylboration reaction proceeding preferentially through transition state A. That is, assuming that R of RCHO has priority over the crotyl group that is transferred, (R,R)-2 and (R,R)-3 invariably produce homoallyl alcohols with S configuration at the carbinol center. The enantiomeric set of homoallylic alcohols are available simply by using reagents (S,S)-2 and (S,S)-3 prepared from (S,S)-DIPT.