Regioselective Reduction of the Homoisoflavone System with Dialkylboranes in the Presence of Palladium Catalysts
作者:Yukio Hoshino、Hiroto Tanaka、Noboru Takeno
DOI:10.1246/bcsj.71.2923
日期:1998.12
(E)-3-Benzylidene-4-chromanones were regioselectively reduced to 3-benzyl-4-chromanones through the 1,4-addition of dialkylboranes, especially 9-borabicyclo[3.3.1]nonane, in excellent yields. The reaction was efficiently promoted by some palladium catalysts. Among them, dichloro[1,1′-bis(diphenylphosphino)ferrocene]palladium(II) was most effective, followed by palladium(II) chloride. Furthermore, the reaction was characteristic of the structurally rigid exo-cyclic α,β-unsaturated ketones, such as (E)-3-benzylidene-4-chromanone, while no reaction occurred in the case of 3-benzyl-4H-chromen-4-one, which is an endo-cyclic one. 2-Benzylidene-3,4-dihydro-1(2H)-naphthalenone and 2-benzylideneindanone were similarly reduced at an olefin moiety only as the result of a 1,4-reduction.
通过二烷基硼烷(尤其是 9-硼杂双环[3.3.1]壬烷)的 1,4-加成反应,(E)-3-亚苄基-4-苯并吡喃酮被区域选择性地还原为 3-苄基-4-苯并吡喃酮,产量极佳。一些钯催化剂有效地促进了该反应。其中,二氯[1,1′-双(二苯基膦)二茂铁]钯(II)最为有效,氯化钯(II)次之。此外,该反应还具有结构坚硬的外环α,β-不饱和酮类(如 (E)-3-benzylidene-4-chromanone )的特征,而内环的 3-benzyl-4H-chromen-4-one 则没有发生反应。2-苄叉-3,4-二氢-1(2H)-萘酮和 2-苄叉茚酮也同样仅在烯烃分子上发生 1,4 还原反应。