Organic Synthesis using the Coupling Reaction of Allylic Esters and Organoborane Ate Complexes

最近我们发现了新的[(MeO)_3 B-R] Li(1)试剂，它在镍催化剂的作用下与烯丙酸酯和碳酸酯发生偶联反应。这些试剂具有高活性，因此二级烯丙基底物可以作为偶联的底物。首先，我们将这些试剂应用于brefeldin a的合成，成功地由4-环戊烯-1,3-二醇单乙酸酯(2)和[（2-呋喃基）- b (OMe)_3] Li （1a）合成了关键中间体，产率高，具有较高的区域选择性和立体选择性。据报道，用经典偶联试剂与醋酸单酯反应会得到不同区域异构体的混合物，因此，本文的成功为以醋酸单酯为起始化合物开辟了新的可能性。在合成过程中，发现了呋喃氧化生成反式4-氧-2-烯醛的新条件，并将其应用于展嘌呤内酯A和pyrenophorin的合成。接下来，我们开发了新的试剂[R-B (Me) (- och (Me) - ch (Me) O-] Li(3)，它比[(MeO)_3B-R] Li(1)在烯丙基偶联中的反应性更强。此外，新试剂首次被发现参与了与芳基甲磺酸酯和位阻顺式1-溴-1-烯-3-醇衍生物的偶联反应，而这两种化合物之前对偶联反应没有反应。

Recently we have found new reagents of [(MeO)_3 B-R] Li (1), which, in the presence of the nickel catalyst, react with coupling with allylic acetates and carbonates. These reagents are high reactive so that secondary allylic substrates can be involved as the substrates in the coupling.First, we applied these reagents to synthesis of brefeldin A.The key intermediate is successfully prepared from 4-cyclopentene-1,3-diol mono acetate (2) and [(2-furyl) -B (OMe)_3] Li (1a) in good yield with high regio- and stereoselectivities. Since reaction of mono acetate 2 using classical coupling reagents are reported to give a mixture of regioisomers, the present success opens a new possibility using the mono acetate 2 as the starting compound. During the synthesis, new conditions of furan oxidation to furnish trans 4-oxo-2-alkenals was found and applied to synthesis of patulolide A and pyrenophorin.Next, we have developed new reagents [R-B (Me) (-OCH (Me) -CH (Me) O-] Li (3), which are more reactive than [(MeO)_3B-R] Li (1) in the allylic coupling. In addition, the new reagents were found for the first time to be participated in the coupling with aryl mesylates and sterically hindered cis 1-bromo-1-alken-3-ol derivatives, both of which are previously unreactive toward the coupling reaction.