Efficient dual catalytic enantioselective diethylzinc addition to the exocyclic CN double bond of some 1,2,4-N-triazinylarylimines using polymer-supported chiral β-amino alcohols derived from norephedrine
作者:Ashraf A. El-Shehawy
DOI:10.1016/j.tet.2007.04.041
日期:2007.6
diethylzinc reagent neither opened the 1,2,4-triazinyl heterocyclic ring nor attacked the carbonyl or the thione groups of the 1,2,4-triazinyl heterocyclic ring and the addition reaction took place exclusively at the exocyclic electrophilic carbon atom yielding the C-ethylated products 4a–f. Reductive cleavage of the 1,2,4-triazinyl heterocyclic ring led smoothly to the corresponding primary aromatic
将手性N,N-二烷基去氧麻黄碱及其相应的共聚物作为对映体选择性二乙基锌的手性配体,除了一些4-亚芳基氨基-3-巯基-6-甲基-4 H -1,2,4-三嗪外环CN双键外-5-ones 2a – f。检查了在标题不对称反应中双催化体系(氨基醇/卤硅烷)的使用。即使在低温下,对映选择性乙基化反应也已在非均相系统中成功进行。相应的4-(1-芳丙基)氨基-3-巯基-6-甲基-4 H -1,2,4-三嗪-5-酮4a – f使用手性聚合物(高达91%ee)以高收率和高对映体选择性获得了苯乙炔,这与从均相类似物(高达92%ee)获得的收率几乎相同。二乙基锌试剂既不打开1,2,4-三嗪基杂环,也不攻击1,2,4-三嗪基杂环的羰基或硫酮基团,加成反应仅在环外亲电子碳原子上发生,从而生成C乙基化产物4a – f。1,2,4-三嗪基杂环的还原裂解平稳地导致相应的伯芳族胺11a – f对映体纯度没有明显损失。还提出了关于加成反应可能的过渡态的建议。