A Convenient Access to γ‐Lactones from
<i>O</i>
‐Allyl‐α‐Bromoesters using a One‐Pot Ionic–Radical–Ionic Sequence
作者:Romain Bénéteau、Jacques Lebreton、Fabrice Dénès
DOI:10.1002/asia.201200212
日期:2012.7
α‐bromo ester precursors with DIBAL‐H and radical cyclization of the resulting O‐aluminum acetals, a preparative in‐situ Oppenauer‐type oxidation of the cyclic O‐aluminum acetal using simple aldehydes or ketones gives access to γ‐lactones in high yields.
An efficient preparation of γ‐lactols and methylene‐γ‐lactols is described. Highly acid‐sensitive lactols are prepared in a concise manner by using a radicalcyclization of aluminumacetals. The precursors for the radical reactions are readily prepared from allyl or propargyl alcohols and α‐bromo acids. Functionalization of the resulting γ‐lactols and methylene‐γ‐lactols can be achieved following isolation
Running rings around aluminum: An efficient procedure for radicalcyclization of α‐bromo esters is reported. Reduction of the esters by DIBAL‐H at low temperature gives aluminumacetals, which are cyclized in the presence of nBu3SnH and Et3B (see scheme). These one‐pot conditions lead to polysubstituted γ‐lactols in high yields, and the mildness of the reaction conditions allows the preparation of
铝周围的滑动环:报道了一种有效的α-溴代酸酯自由基环化的方法。在低温下通过DIBAL-H还原酯得到铝缩醛,缩醛在n Bu 3 SnH和Et 3 B存在下环化(参见方案)。这些一锅条件可高产率地产生多取代的γ-内酯,反应条件温和,可制备酸敏感的衍生物。