1,3-Diethynylallenes: Carbon-Rich Modules for Three-Dimensional Acetylenic Scaffolding
1,3-Diethynylallenes: Carbon-Rich Modules for Three-Dimensional Acetylenic Scaffolding
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DOI：
10.1002/1522-2675(200210)85:10
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发表时间：
2002-10
影响因子：
1.8
通讯作者：
R. Livingston;L. Cox;Severin Odermatt;F. Diederich
中科院分区：
文献类型：
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作者：
R. Livingston;L. Cox;Severin Odermatt;F. Diederich
0催化的双丙炔基与硅基保护的炔的交叉偶联，提供了多种1,3-二乙基烯的途径，这是一种新的三维乙基支架模块家族。在对映体纯形式下，这些富含c的构建块可以通过氧化寡聚提供一种迷人的新型螺旋低聚物和全碳骨架聚合物（图2）。在第一种方法中，双丙基环氧化物在s2型交叉偶联过程中开环，得到硅基保护的烷氧化合物，提供1,3-二乙基烯（）-8、（）-12（方案3）和（）-15（方案5）。一种更普遍的方法是采用双丙酯碳酸酯或酯作为底物（方案6±8），并将该方法应用于制备一系列1,3二乙基烯，以研究它们对不良环加成的总体稳定性如何受到烯端取代基性质的影响[22]。研究表明，1,3-二乙基亚烯发色团只有在空间体保护和避免额外的电子离域时才能稳定地抵抗[22]环加成。与双丙基底物交叉偶联的区域选择性完全由位阻因素控制：攻击发生在含有较小取代基的炔基部分（方案9和方案10）。末端不受保护的1,3-二乙基亚烯（）-49的氧化Hay偶联产生了第一个二聚体50，可能是两个非对映异构体的混合物（方案12）。用新方法制备硅基保护的四乙基亚烯的尝试失败了（方案13）。对照实验（方案14±16）表明，在合成这种尚不明确的发色团时，Pd -催化的与丁二炔部分的交叉偶联需要强制条件，在这种条件下，初始产物的快速环加成是无法避免的[22]。
0-catalyzed cross-coupling of substrates, which bear bispropargylic leaving groups with silyl-protected alkynes, has provided access to a variety of 1,3-diethynylallenes, a new family of modules for three-dimensional acetylenic scaffolding. In enantiomerically pure form, these C-rich building blocks could provide access ± by oxidative oligomerization ± to a fascinating new class of helical oligomers and polymers with all-carbon backbones (Fig. 2). In the first of two routes, a bispropargylic epoxide underwent ring opening during S2-type cross-coupling, and the resulting alkoxide was silyl-protected, providing 1,3-diethynylallenes ()-8, ()-12 (Scheme 3), and ()-15 (Scheme 5). A more general approach involved bispropargylic carbonates or esters as substrates (Scheme 6 ± 8), and this route was applied to the preparation of a series of 1,3diethynylallenes to investigate how their overall stability against undesirable [2 2] cycloaddition is affected by the nature of the substituents at the allene moiety. The investigation showed that the 1,3-diethynylallene chromophore is stable against [2 2] cycloaddition only when protected by steric bulk and when additional electron delocalization is avoided. The regioselectivity of the cross-coupling to the bispropargylic substrates is entirely controlled by steric factors: attack occurs at the alkyne moiety bearing the smaller substituent (Schemes 9 and 10). Oxidative Hay coupling of the terminally mono-deprotected 1,3-diethynylallene ()-49 afforded the first dimer 50, probably as a mixture of two diastereoisomers (Scheme 12). Attempts to prepare a silyl-protected tetraethynylallene by the new methodology failed (Scheme 13). Control experiments (Schemes 14 ± 16) showed that the Pd 0 -catalyzed cross-coupling to butadiyne moieties in the synthesis of this still-elusive chromophore requires forcing conditions under which rapid [2 2] cycloaddition of the initial product cannot be avoided.