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

最近我们发现了新的试剂[(MeO)_3B-R]Li(1)，它在镍催化剂存在下与烯丙基乙酸酯和碳酸酯发生偶联反应。首先，我们将这些试剂应用于灯盏花素A的合成。关键中间体4-环戊烯-1，3-二醇单乙酸酯(2)和[(2-呋喃)-B(OMe)_3]Li(1a)以较高的产率和较高的区域和立体选择性合成了关键中间体。由于报道了用经典偶联剂与单乙酸酯2反应生成区域异构体的混合物，目前的成功开启了以单乙酸酯2为起始化合物的新的可能性。在合成过程中，我们发现了呋喃氧化生成反式4-氧代-2-烯烃的新条件，并将其应用于棒状内酯A和立枯草红素的合成。其次，我们开发了新试剂[R-B(Me)(-Och(Me)-CH(Me)O-]Li(3))，它们在烯丙基偶联反应中比[(MeO)_3B-R]Li(1)更具活性。此外，首次发现新试剂参与了与芳基甲磺酸酯和空间受阻的顺式1-溴-1-烷基-3-醇衍生物的偶联反应，这两种化合物以前对偶联反应都没有反应。

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.