Design of Chiral NHC‐Carboxylates as Potential Ligands for Pd‐Catalyzed Enantioselective C−H Activation
作者:Nadja E. Niggli、Olivier Baudoin
DOI:10.1002/hlca.202100015
日期:2021.3
Despite numerous efforts, the synthesis of scalemic carbo‐ and heterocycles through Pd0‐catalyzed C(sp3)−H activation employing chiral ancillary ligands or chiral bases is still limited. Inspired by the recently reported outstanding performance of IBiox‐type NHC ligands and bifunctional ligands in similar transformations, a new class of bifunctional NHC‐ligands bearing a pendant carboxylate group was
tetrahydrobenzo[a]heptalenes 23a-d (Scheme7 and 8). Reaction of 23a-d with 2 equiv. of triphenylmethylium tetrafluoroborate in boiling CHCl3, followed by treatment with Me3N in CH2Cl2, generated directly 2, unfortunately in a mixture with Ph3CH that could not be separated from 2 (Scheme 10 and 11). The second approach via dimethyl benzo[a]heptalene-6,7-dicarboxylate (30) (Scheme 12) that was gradually
苯并[ a ]庚烷已通过两种不同的方法合成。第一个遵循的是通往六氢苯并[ a ]庚烯酮19a的途径,该途径已由Wenkert和Kim(Scheme)进行了描述。实际上,图19A与它的混合物,得到双键移位异构体19b中。将该混合物还原成相应的仲醇26a / 26b并消除H 2 O,得到四氢苯并[ a ]庚烷23a-d的混合物(方案7和8)。23a-d与2当量的反应。在沸腾的CHCl 3中加入四氟硼酸三苯基甲基钾盐,然后在CH 2 Cl 2中用Me 3 N处理,直接生成2,不幸的是在无法与2分离的Ph 3 CH混合物中(方案10和11)。通过苯并[ a ]庚二烯-6,7-二羧酸二甲酯(30)(方案12)的第二种方法逐渐转化为相应的甲醛37和43(方案14),在130℃下用威尔金森催化剂[RhCl(PPh 3)3 ]在甲苯中处理后,将两者平滑脱羰,最终得到纯的2,为不稳定的橙色粘性油。讨论了2的UV
Nonacethrene Unchained: A Cascade to Chiral Contorted Conjugated Hydrocarbon with Two sp<sup>3</sup>-Defects
diradicaloid nonacethrene to give a chiral contorted polycyclicaromatichydrocarbon named hypercethrene. In this ten-electron oxidation process, four σ-bonds, one π-bond, and three six-membered rings are formed in a sequence of up to nine steps to yield a 72-carbon-atom warped framework, comprising two configurationally locked [7]helicene units, a fluorescent peropyrene unit, and two precisely installed sp3-defects