Stereoselective benzylic α-acylamino radical cyclisation: a model study for the Tacaman indole alkaloid skeleton
作者:Rainer Clauss、Roger Hunter
DOI:10.1039/a602932i
日期:——
Radical cyclisation with tributyltin hydride of the
α-phenylsulfanyl lactam 6, prepared in nine steps from
D-ribose via the corresponding phthalimide, gives
the all-cis tetrahydropyrido[2,1-a]isoindolone 7
stereoselectively as the major diastereomer. The structure of the
product is established by 1H NMR spectroscopy and
corroborated by formation of the cis-lactone 8. The
diastereoselectivity is shown to be controlled by the
allylic/homoallylic cis-ketal group, and a transition state is
proposed. The sequence constitutes the first simple model study for C/D
ring fusion of the Tacaman indole alkaloid skeleton via the
relatively unexplored C-3âC-14 bond disconnection.
由 D-核糖通过相应的邻苯二甲酰亚胺分九步制备的δ-苯硫内酰胺 6 与三丁基氢化锡发生辐射环化反应,立体选择性地得到了全顺式四氢吡啶并[2,1-a]异吲哚酮 7 的主要非对映异构体。通过 1H NMR 光谱确定了产物的结构,并通过形成顺式内酯 8 得到证实。结果表明,非对映选择性受烯丙基/高烯丙基顺式酮基的控制,并提出了一种过渡态。该序列是对 Tacaman 吲哚生物碱骨架通过相对未探索的 C-3âC-14 键断开进行 C/D 环融合的首次简单模型研究。