S_N2-Selective allylic substitution of chiral γ-aryl substituted allylic picolinates with alkynylcopper reagents

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• 作者：Qian Wang ; Yuichi Kobayashi
• 关键词：Allylic substitution ; Picolinate ; Acetylene ; Solvent effect ; CH₂Cl₂
• 刊名：Tetrahedron Letters
• 出版年：2010
• 出版时间：20 October 2010
• 年：2010
• 卷：51
• 期：42
• 页码：5592-5595
• 全文大小：446 K

文摘

Substitution of γ-aryl secondary allylic picolinates with alkynyl copper reagents was studied. The copper reagent, prepared from TMSCCMgBr and CuBr·Me₂S in 2:1, was subjected to substitution of the picolinate derived from (E)-3-phenyl-1-methyl-2-propenyl alcohol at 0 °C for 1 h in THF to produce a mixture of α- and γ-products and the alcohol in 67:20:13, while the reagent in 3 or 4:1 ratio gave the α-product with 90–91 % selectivity. On the contrary, reaction in CH₂Cl₂–THF (6–8:1) at 0 °C for 1 h furnished the α-product with 99 % regioselectivity. The effect of CH₂Cl₂ was also demonstrated with eight more examples. Furthermore, 99 % inversion was determined by transformation to the literature compound and by chiral HPLC.