Atroposelectivity in the electrophilic substitution reactions of laterally lithiated and silylated tertiary amides
作者:Jonathan Clayden、Jennifer H. Pink、Neil Westlund、Christopher S. Frampton
DOI:10.1039/b200358a
日期:2002.3.25
Lateral lithiation–electrophilic quench of 2-alkyl-1-naphthamides and 2,6-dialkylbenzamides yields products containing an atropisomeric Ar–CO axis and a new stereogenic centre with high (generally >95 ∶ 5) diastereoselectivity. With imines as electrophiles, single diastereoisomers containing an atropisomeric axis and two new stereogenic centres are formed. 2,6-Dialkylbenzamides may be functionalised stereoselectively at both the 2- and 6-positions, leading (with imines) to symmetrical compounds bearing 1,7-related stereogenic centres. 2-Alkylbenzamides with only one ortho alkyl group are not atropisomeric at ambient temperature but are functionalised diastereoselectively by lateral lithiation–electrophilic quench at −78 °C. Stabilisation of the atropisomeric products by further lithiation and alkylation proves their diastereoselective formation. The lack of stereospecificity in the fluoride-promoted reaction of a laterally silylated
1-naphthamide with an aldehyde suggests that reported reactions of laterally silylated benzamides may also be controlled by the rotationally restricted amide group.
侧向锂化-亲电淬灭2-烷基-1-萘酰胺和2,6-二烷基苯甲酰胺可以得到含有轴向手性Ar–CO和新的手性中心的产品,具有高(通常>95∶5)的非对映选择性。以亚胺为亲电试剂时,会形成含有一个轴向手性和两个新的手性中心的单一非对映异构体。2,6-二烷基苯甲酰胺可以在2-和6-位置上进行立体选择性功能化,从而(与亚胺反应)形成具有1,7-相关手性中心的对称化合物。单个邻位烷基的2-烷基苯甲酰胺在室温下不是轴向手性的,但在-78°C下通过侧向锂化-亲电淬灭可以非对映选择性地进行功能化。通过进一步锂化和烷基化稳定轴向手性产物证实了其非对映选择性的形成。侧向硅烷化的1-萘酰胺与醛的氟化促进反应缺乏立体专一性,表明报道的侧向硅烷化苯甲酰胺反应也可能受到转动受限的酰胺基团的控制。