Samarium(II)-mediated 4-exo-trig cyclisations of unsaturated aldehydes. A stereoselective approach to functionalised cyclobutanols
作者:Derek Johnston、Catherine F. McCusker、Kenneth Muir、David J. Procter
DOI:10.1039/a909549g
日期:——
γ,δ-Unsaturated aldehydes having a fully substituted centre in either the α- or β-positions, have been prepared from substituted γ-butyrolactones and undergo efficient 4-exo-trig cyclisation on treatment with samarium(II) iodide to give functionalised cyclobutanols. In all cases cyclisation occurs with complete diastereocontrol to give anti-cyclobutanol products. The stereochemistry of the products has been confirmed by NOE and X-ray crystallographic studies. In the cyclisation of substrates having a third substituent on the double bond, α- to the ester, significant control is achieved at the third newly formed stereocentre lying outside the ring. The origin of the stereoselectivity at this third centre and its marked dependence on cosolvent are discussed.
γ,δ-不饱和醛具有完全取代的中心,无论是在α-还是β-位置,均是通过取代的γ-丁内酯制备的,并在处理时与锶(II)碘化物发生高效的4-exo-trig环化反应,生成功能化的环丁醇。在所有情况下,环化反应都以完全的非对映选择性进行,生成反式环丁醇产物。产物的立体化学已通过NOE和X射线晶体学研究得到确认。在具有双键上第三个取代基的底物的环化反应中,位于环外的新形成的第三个立体中心实现了显著的控制。讨论了该第三个中心的立体选择性的来源及其对共溶剂的显著依赖性。