我们报告了未活化的1,6-二炔与N-溴代琥珀酰亚胺(NBS)的Pd催化卤代环化反应。这种方法可生产立体定义明确的二溴取代的二氢吡喃,四氢吡啶和3-亚甲基环己烯,并带有环外双键附件,且收率很高。发现铜盐是该反应中有用的路易斯酸。从机理上讲,提出了一种形式上的抗碳氢键合和溴化物自由基促进的Pd II -Pd III -Pd I -Pd II催化循环,参与了二溴取代产物的形成。将二氢吡喃衍生物进一步官能化后进行B(C 6 F 5)3-催化的开环并还原得到具有优异立体选择性的二溴代1,3-二烯。
A highly enantioselective intermolecular [2+2+2] cycloaddition of alkynes was catalyzed by a chiral iridium complex. Symmetrical and unsymmetrical diynes, and monoalkynes possessing functional group(s) were subjected to the reaction and various types of axiallychiral compounds possessing biaryl skeletons were obtained in good to excellent enantiomeric excesses.
An asymmetric [2+2+2] cycloaddition of an alpha,omega-diyne, possessing ortho-substituted aryl groups on its terminus, and a monoalkyne with oxygen functionalities gave various axially chiral teraryl compounds. The coupling proceeded with extremely high enantio- (>99.5% ee) and diastereoselectivities (dl/meso = >95/5) when catalyzed by an iridium-chiral phosphine complex. As the products were readily transformed into diol compounds by deprotection without racemization, the present procedure provides access to a new chiral pool of diol compounds with C2 symmetry.