Rapid assembly of complex cyclopentanes employing chiral, α,β-unsaturated acylammonium intermediates
作者:Gang Liu、Morgan E. Shirley、Khoi N. Van、Rae Lynn McFarlin、Daniel Romo
DOI:10.1038/nchem.1788
日期:2013.12
With the intention of improving synthetic efficiency, organic chemists have turned to bioinspired organocascade or domino processes that generate multiple bonds and stereocentres in a single operation. However, despite the great importance of substituted cyclopentanes, given their prevalence in complex natural products and pharmaceutical agents, the rapid, enantioselective assembly of these carbocycles lags behind cyclohexanes. Here, we describe a Michaelâaldol-β-lactonization organocascade process for the synthesis of complex cyclopentanes utilizing chiral α,β-unsaturated acylammonium intermediates, readily generated by activation of commodity unsaturated acid chlorides with chiral isothiourea catalysts. This efficient methodology enables the construction of two CâC bonds, one CâO bond, two rings and up to three contiguous stereogenic centres delivering complex cyclopentanes with high levels of relative and absolute stereocontrol. Our results suggest that α,β-unsaturated acylammonium intermediates have broad utility for the design of organocascade and multicomponent processes, with the latter demonstrated by a MichaelâMichaelâaldol-β-lactonization. Despite their appearance in a number of bioactive natural products, the synthesis of 5-membered carbocycles has received much less attention than synthesis of their 6-membered counterparts. Here, a Michael-aldol-β-lactonization cascade is used to forge two C-C bonds, one C-O bond, two rings and up to three contiguous stereocentres and deliver complex cyclopentanes with high levels of relative and absolute stereocontrol.
为了提高合成效率,有机化学家转而采用生物启发的有机级联或多米诺过程,在一次操作中生成多个键和立体中心。然而,尽管取代的环戊烷在复杂的天然产品和药物制剂中非常普遍,具有重要意义,但这些碳环的快速对映选择性组装却落后于环己烷。在这里,我们介绍了利用手性δ,δ²-不饱和酰基铵中间体合成复杂环戊烷的迈克尔-醛-δ-内酯化有机级联工艺,这种中间体可通过手性异硫脲催化剂活化商品不饱和酸氯化物而生成。这种高效的方法可以构建两个 CâC 键、一个 CâO 键、两个环和多达三个连续的立体中心,从而提供具有高度相对和绝对立体控制能力的复杂环戊烷。我们的研究结果表明,δ,δ-不饱和酰基铵中间体在设计有机级联和多组分过程中具有广泛的用途,后者通过迈克尔-迈克尔醛-δ-内酯化过程得到了证明。尽管五元碳环出现在许多具有生物活性的天然产物中,但其合成所受到的关注却远远低于六元碳环的合成。在这里,我们利用迈克尔-醛-δ-内酯化级联法生成了两个 C-C 键、一个 C-O 键、两个环和多达三个连续的立体中心,并提供了具有高水平相对和绝对立体控制的复杂环戊烷。