Stereo‐ and Chemodivergent NHC‐Promoted Functionalisation of Arylalkylketenes with Chloral
作者:James J. Douglas、Gwydion Churchill、Alexandra M. Z. Slawin、David J. Fox、Andrew D. Smith
DOI:10.1002/chem.201503308
日期:2015.11.9
Stereo‐ and chemodivergent enantioselective reaction pathways are observed upon treatment of alkylarylketenes and trichloroacetaldehyde (chloral) with N‐heterocyclic carbenes, giving selectively either β‐lactones (up to 88:12 dr, up to 94 % ee) or α‐chloroesters (up to 94 % ee). Either 2‐arylsubstitution or an α‐branched iPr alkyl substituent within the ketene favours the chlorination pathway, allowing
用N-杂环卡宾处理烷基芳基烯酮和三氯乙醛(氯代)时,观察到立体和化学发散对映选择性反应途径,选择性地产生β-内酯(高达88:12 dr,高达94% ee)或α-氯代酯(高达至94% ee)。乙烯酮中的2-芳基取代或α-支链的i Pr烷基取代基都有利于氯化途径,从而使氯醛可以在不对称催化中用作亲电子氯化试剂。