Acta Chimica Sinica ›› 2019, Vol. 77 ›› Issue (9): 927-931.DOI: 10.6023/A19040151 Previous Articles     Next Articles

Special Issue: 有机自由基化学



赵琦, 屠树江*(), 姜波*()   

  1. 江苏师范大学化学与材料科学学院 徐州 221116
  • 投稿日期:2019-04-30 发布日期:2019-06-21
  • 通讯作者: 屠树江,姜波;
  • 基金资助:
    项目受国家自然科学基金(No. 21871112);江苏省青蓝工程资助(No. QL2016006)

Hydrogen Radical Initiated 1,2-Alkynyl Migration

Zhao, Qi, Tu, Shu-Jiang*(), Jiang, Bo*()   

  1. School of Chemistry and Material Science, Jiangsu Normal University, Xuzhou 221116
  • Received:2019-04-30 Published:2019-06-21
  • Contact: Tu, Shu-Jiang,Jiang, Bo;
  • Supported by:
    Project supported by the National Natural Science Foundation of China(No. 21871112);the Qing Lan Project of Jiangsu Education Committee(No. QL2016006)

As inexpensive and readily available feedstocks, alkenes possess a unique reactivity profile and thus have been extensively applied in synthetic chemistry. Specifically, radical-triggered difunctionalization of alkenes provides a valuable synthetic strategy for their high utilization by incorporating two functional groups across the C=C π system. Despite the great achievements gained in this field, the vast majority of well-developed methods generally focus on activated alkenes, because its nascent alkyl radical needs to be stabilized by adjacent functional groups (e.g. aryl, carbonyl, heteroatom) via p-π conjugate effect. However, radical induced difunctionalization of unactivated alkenes remains elusive. Herein, a new protocol for Fe(III) mediated hydroalkynylation of unactivated olefins is reported. By using the characteristics of the in-situ-generated hydrogen radical from the interaction of Fe(acac)3 and phenylsilane, hydrogen radical-triggered intramolecular 1,2-alkynyl migration was realized in this reaction, which led to the synthesis of a series of α-alkynyl ketones with moderate to good yields. Based on the experimental results and literature reports, a reasonable reaction mechanism was proposed, which involved hydrogen radical addition, 3-exo-dig cyclization (anti-Baldwin rules) and C—C bond breaking/recombination. Moreover, the reaction features good tolerance of functional groups, in which estrone-derived 1,4-enyne could be accommodated. A typical procedure for hydroalkynylation of unactivated alkenes is as follows: Fe(acac)3 (1.2 equiv., 0.24 mmol) and NaHCO3 (1.0 equiv., 0.2 mmol) are added to the 10-mL pressure tube. Then 1,4-enynes (1.0 equiv., 0.2 mmol) and phenylsilane (2.0 equiv., 0.4 mmol) are dissolved in 1.0 mL ethyl alcohol, respectively. Both of them are injected into this vial. The reaction system was sealed and stirred at 100 ℃ until the 1,4-enynes consumed that is determined by thin layer chromatography (TLC). After the reaction completes, the resulting mixture is extracted with EtOAc for three times, then the organic phase is concentrated and evaporated on a rotary evaporator. The residue was purified by chromatography on silica gel with petroleum ether/ethyl acetate (VV=75∶1) as the eluent to afford α-alkynyl ketones.

Key words: hydroalkynylation of unactivated alkene, Baldwin rule, alkynyl migration, 1,4-enyne, α-alkynyl ketone