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

最近，我们发现了新的[（MeO）_3B-R] Li（1）试剂，它在镍催化剂存在下与乙酸烯丙酯和碳酸烯丙酯发生偶联反应。首先，我们将这些试剂应用于布雷菲德菌素A的合成，成功地以4-环戊烯-1，3-二醇单乙酸酯（2）和[（2-呋喃基）-B（OMe）_3] Li（1a）为原料合成了布雷菲德菌素A。由于报道了使用经典偶联试剂的单乙酸酯2的反应得到区域异构体的混合物，因此目前的成功开辟了使用单乙酸酯2作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-烯醛的新反应条件，并将其应用于patulatinA和pyrenophorin的合成，同时我们还开发了新的反应试剂[R-B（Me）（-OCH（Me）-CH（Me）O-] Li（3），它比[（MeO）_3B-R] Li（1）在烯丙基偶联反应中的反应活性更高。此外，首次发现新试剂参与与甲磺酸芳基酯和空间位阻的顺式1-溴-1-阿尔肯-3-醇衍生物的偶联，这两种化合物以前对偶联反应不起反应。

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.