Department of Chemistry, University of Illinois at Chicago, 845 West Taylor Street, Chicago, IL, 60607, USA.
College of Chemistry and Materials Engineering, Wenzhou University, Wenzhou, Zhejiang Province, 325035, P.R. China.
Angew Chem Int Ed Engl. 2016 Jan 18;55(3):1151-5. doi: 10.1002/anie.201510006. Epub 2015 Dec 4.
Substituent- and oxidant-dependent transformations of allenes are described. Given the profound influence of the substituent on the reactivity of allenes, the subtle differences in allene structures are manifested in the formation of diverse products when reacted with different electrophiles/oxidants. In general, reactions of nonsilylated allenes involve an allylic cation intermediate by forming a C-O bond, at the sp-hybridized C2, with either DDQ (2,3-dichloro-5,6-dicyano-p-benzoquinone) or TBHP (tert-butyl hydroperoxide), along with FeCl2⋅4 H2O (10 mol %). In contrast, silylated allenes favor the formation of propargylic cation intermediates by transferring the allenic hydride to the oxidant, thus generating 1,3-enynes (E1 product) or propargylic THBP ethers (S(N)1 product). The formation of these different putative cationic intermediates from nonsilylated and silylated allenes is strongly supported by DFT calculations.
描述了烯丙基取代基和氧化剂依赖性的转化。考虑到取代基对烯丙基反应性的深远影响，当与不同的亲电试剂/氧化剂反应时，烯丙基结构的细微差异表现为形成不同的产物。一般来说，未硅烷基化的烯丙基反应涉及通过形成 C-O 键，在 sp 杂化的 C2 上，与 DDQ（2,3-二氯-5,6-二氰基对苯醌）或 TBHP（叔丁基过氧化物），以及 FeCl2⋅4H2O（10 mol%），形成烯丙基阳离子中间体。相比之下，硅烷基化的烯丙基通过将烯丙基氢化物转移到氧化剂上来有利于形成丙炔基阳离子中间体，从而生成 1,3-烯炔（E1 产物）或丙炔基 THBP 醚（S（N）1 产物）。DFT 计算强烈支持了从未硅烷基化和硅烷基化的烯丙基形成这些不同的假定阳离子中间体。
