Department of Chemistry, University of Oxford, Chemistry Research Laboratory, 12 Mansfield Road, Oxford OX1 3TA, U.K.
Org Lett. 2019 Sep 6;21(17):6663-6667. doi: 10.1021/acs.orglett.9b02119. Epub 2019 Aug 9.
The catalytic reductive transformation of carboxylic esters into α-branched ethers is described. The procedure pivots on the chemoselective iridium-catalyzed hydrosilylation of ester and lactone functionality to afford a silyl acetal intermediate. Upon treatment with a Lewis acid, these hemilabile intermediates dissociate to form reactive oxocarbenium ions, which can be intercepted by allyltributyltin nucleophiles, resulting in the formation of valuable α-branched alkyl-alkyl ether derivatives. This reductive allylation procedure was found to be amenable to a range of carboxylic ester starting materials, and good chemoselectivity for ethyl over -butyl esters was demonstrated. Furthermore, downstream synthetic manipulation of α-amino acid-derived products led to the efficient formation of pyrrolidine, piperidine, and azepane frameworks.
描述了羧酸酯向α-支链醚的催化还原转化。该方法的关键在于选择性的铱催化酯和内酯的硅氢化反应，得到硅基缩醛中间体。用路易斯酸处理时，这些半稳定中间体解离形成反应性氧杂碳翁离子，可被烯丙基三丁基锡亲核试剂捕获，形成有价值的α-支链烷基-烷基醚衍生物。该还原烯丙基化反应适用于多种羧酸酯起始原料，并且对乙酯和叔丁酯表现出良好的化学选择性。此外，α-氨基酸衍生产物的下游合成操作可有效地形成吡咯烷、哌啶和氮杂环庚烷骨架。
