Effects of olefin geometry on the stereochemistry of Lewis acid mediated additions of crotylstannanes to aldehydes
Effects of olefin geometry on the stereochemistry of Lewis acid mediated additions of crotylstannanes to aldehydes
复制标题
烯烃几何形状对路易斯酸介导的巴豆基锡烷与醛的立体化学加成的影响
DOI：
10.1021/jo00104a054
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发表时间：
1994
影响因子：
3.6
通讯作者：
D. E. Abbott
中科院分区：
文献类型：
--
作者：
G. Keck;K. Savin;E. Cressman;D. E. Abbott
双键几何形状（E/Z立体化学）在巴豆基锡烷与醛的反应中的作用已经针对代表性的“简单”、α-烷氧基和β-烷氧基醛进行了检查。对于由BF 3·Et 2 O介导的巴豆基锡烷与简单的非手性脂族、芳族或α 1/3不饱和醛的反应，使用E巴豆基锡烷给出了比用Z获得的顺式选择性高得多的顺式选择性（例如，43：1相对于用苯甲醛的4：1）。一个向斜过渡态，其中CH 2SnBu 3基团是笨拙的氧提出来解释这些结果。对于α-烷氧基醛，E锡烷与MgBr 2的使用给出了最高的顺式选择性，而Z锡烷与β-烷氧基底物的立体选择性略好。相比之下，使用TiCl 4优先从E锡烷和α或β-烷氧基底物得到反式产物。
The role of the double bond geometry (E/Z stereochemistry) in reactions of crotylstannanes with aldehydes has been examined for representative “simple”, a-alkoxy, and/3-alkoxy aldehydes. For the reaction of crotylstannane with simple achiral aliphatic, aromatic, or a,/3 unsaturated aldehydes mediated by BF3'Et20, use of the E crotylstannane gives much enhanced syn selectivity over that obtained with Z (eg, 43: 1 vs 4: 1 with benzaldehyde). A synclinal transition state in which the CH2SnBu3 group is gauche to oxygen is proposed to explain these results. For a-alkoxy aldehydes, use of the E stannane with MgBr2 gives the highest syn selectivity, while the Z stannane gives slightly better stereoselectivity with/3-alkoxy substrates. In contrast, the use of TiCU gives anti products preferentially from the E stannane and either a or/3-alkoxy substrates.