4,5-diisopropyl-B-[(E)-[(3'-menthofuryl)dimethylsilyl]allyl]-1,3,2-dioxaborolane, an improved chiral reagent for the anti alpha-hydroxyallylation of aldehydes: Application to the enantioselective synthesis of (-)-swainsonine
4,5-diisopropyl-B-[(E)-[(3'-menthofuryl)dimethylsilyl]allyl]-1,3,2-dioxaborolane, an improved chiral reagent for the anti alpha-hydroxyallylation of aldehydes: Application to the enantioselective synthesis of (-)-swainsonine
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DOI：
10.1021/jo961840s
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发表时间：
1997-02-21
影响因子：
3.6
通讯作者：
Roush, WR
中科院分区：
文献类型：
--
作者：
Hunt, JA;Roush, WR
酒石酸二异丙酯修饰的（E）-[γ-（呋喃基二甲基硅基）烯丙基]硼酸酯10和11被设计用于通过醛的反-α-羟基烯丙基化反应对映选择性合成取代的反-3，4-二羟基-1-丁烯9。醛与10和11的反应提供了具有良好的对映选择性（74- 82%ee）的呋喃基二甲基硅烷基取代的反式-1，2-硅醇1,2和13，并且通过改进的Fleming-Tamao氧化方案将硅醇氧化为相应的反式-1，2-二醇9。（薄荷基）硅烷单元对亲电取代的高反应性允许薄荷基取代的硅烷醇13的完全脱甲硅烷基化和随后在一锅操作中氧化成二醇9，而不竞争烯丙基硅烷单元的脱甲硅烷基化。然而，对于与三种手性醛23-35的反应性较低的2-（5-甲基）-不对称反应的脱甲硅烷基化-氧化需要两步方案（80至> 92%de，除了与醛25的错配反应，其基本上是非选择性的）。然而，[2-（5-甲基呋喃基）]二甲基甲硅烷基]烯丙基]硼酸酯10只能以小于或等于15%的产率合成，并且2-（5-甲基呋喃基）取代的硅烷醇12的氧化比相应的薄荷呋喃基取代的硅烷醇13的氧化产率低。因此，酒石酸二异丙酯改性的（E）-[γ-[（薄荷基）二甲基甲硅烷基]烯丙基]硼酸酯11被证明是两种试剂中更有用的。作为11在多羟基化天然产物合成中的效用的证明，这种新试剂用于天然存在的生物碱（-）-苦马豆素的简单和高度立体选择性的合成（42）。
Diisopropyl tartrate-modified (E)-[gamma-(furyldimethylsilyl)allyl]boronates 10 and 11 were designed for the enantioselective synthesis of substituted anti-3,4-dihydroxy-1-butenes 9 via the anti-alpha-hydroxyallylation of aldehydes. The reactions of aldehydes with 10 and 11 provided furyldimethylsilyl-substituted anti-1,2-silanols 12 and 13 with good enantioselectivity (74-82% ee), and the silanols were oxidized to the corresponding anti-1,2-diols 9 by a modified Fleming-Tamao oxidation protocol. The high reactivity of the (menthofuryl)silane unit toward electrophilic substitution allowed complete protodesilylation of menthofuryl-substituted silanols 13 and subsequent oxidation to diols 9 in a one-pot operation without competing protodesilylation of the allylsilane unit. However, a two-step protocol was required for the protodesilylation-oxidation of the less reactive 2-(5-methyl)-asymmetric reactions with three chiral aldehydes 23-35 (80 to >92% de, with the exception of the mismatched reactions with aldehyde 25, which were essentially unselective). However, [[[2-(5-methylfuryl)]dimethylsilyl]ally]boronate 10 could only be synthesized in less than or equal to 15% yield, and oxidations of the 2-(5-methylfuryl)-substituted silanols 12 were lower-yielding than oxidations of the corresponding menthofuryl-substituted silanols 13. Thus diisopropyl tartrate-modified (E)-[gamma-[(menthofuryl)dimethylsilyl]ally]boronate 11 proved to be the more useful of the two reagents. As a demonstration of the utility of 11 in the synthesis of polyhydroxylated natural products, this new reagent was used in a brief and highly stereoselective synthesis of the naturally occurring alkaloid (-)-swainsonine (42).