New Method of Radical Formation and Its Application to Organic Synthesis

一种新的高效生成有机自由基的方法已被应用于有机合成中。三乙基硼烷引发的三苯基锡烷与乙炔的加成反应在高区域选择性和立体选择性下进行顺利。应用于在适当位置含有烯烃键的乙炔，可立体选择性地得到环化产物；三苯基锡自由基选择性地攻击乙炔键生成乙烯基自由基，乙烯基自由基在分子内立体选择性地加入烯烃。三苯基日耳曼在三乙基硼烷催化下与1-炔加成。在这种情况下，反应的动力学控制在-78ºC，产生z -异构体，而反应的热力学控制在60ºC，主要产生异构体。通过对上述反应的机理研究，提出了一种有效的烯烃几何异构化方法。烷基卤化物可以通过自由基型还原还原为相应的碳氢化合物。分子内加成的烷氧基硫羰基自由基，相当于酰基自由基，得到-亚甲基内酯。在三乙基硼烷催化下，碘化烷基顺利加入乙炔，生成区域选择性和立体选择性碘化乙烯。全氟烷基碘化物类似地加入乙炔。在三乙基硼烷存在下，-溴酮与羰基化合物反应得到Reformatsky型反应产物；硼烯酸酯的形成并与醛反应生成醛醇产物。三乙基硼烷介导的碘化烷基与甲基乙烯酮的加成也得到硼烯酸酯。当得到的硼烯醇酯与醛反应生成醛醇产物时，上述反应开启了碘化烷基、甲基乙烯酮和醛的新型三组分偶联反应。

Novel efficient method for the generation of organic radical species has been applied to organic syntheses. Triethylborane-initiated addition of triphenylstannane to acetylenes proceeds smoothly in high regio- and stereoselectivity. Application to an acetylene containing an olefinic bond at appropriate position provides a cyclized product stereoselectively; triphenyltin radical attacks at acetylene bond regioselectively to give a vinyl radical, which adds intramolecularly to an olefin stereoselectively. Triphenylgermane adds to a 1-alkyne under triethylborane catalysis. In this case, reaction is kinetically controlled at -78ﾟC to give Z-isomer, whereas reaction is thermodynamically controlled at 60ﾟC affording Enisomer predominantly. By the mechanistic investigation of the above reaction, an efficient procedure of the isomerization of olefin geometry has been devised. Alkyl halides can be reduced to the corresponding hydrocarbons by radical type reduction. Intramolecular addition of alkoxythiocarbonyl radical, an acyl radical equivalent, gives an -methylene lactone. Alkyl iodides add to acetylene smoothly under triethylborane catalysis to give vinyl iodides regio- and stereoselectively. Perfluoroalkyl iodides add to acetylenes analogously. Reaction of an -bromo ketone with a carbonyl compound in the presence of triethylborane gives a Reformatsky type reaction product; formation of boron enolate and reaction with aldehyde to give an aldol product. Triethylborane-mediated addition of an alkyl iodide to methyl vinyl ketone also gives a boron enolate. As the obtained boron enolate reacts with an aldehyde to give aldol product, the above reactions opens novel three components coupling reaction of alkyl iodide, methyl vinyl ketone, and aldehyde.