Development of Novel Reformatsky Reaction by Using Lewis Acid-Reductant.

我们发现，在温和的条件下，Lewis酸和磷化氢结合可以实现α-溴酰胺的还原。此外，已有报道称，当醛与中间体金属烯醇酯反应时，可进行reformatsky型反应，以高立体选择性的收率得到所需的β-羟酰胺。在本研究中，我们希望利用这种方法来开发合成上有用的反应。首先，研究了用α-溴酮或硫酯代替α-溴酰胺的Reformatsky反应。结果表明，采用四氯化钛与三邻甲基膦的结合，得到了收率高、立体选择性好的reformatsky型产物。接下来，将该反应应用于其他亲电试剂，如硫酯、缩醛和亚胺。与硫酯的反应顺利地得到了还原-克莱森缩合物，与亚胺的曼尼希反应也得到了相应的加合物，收率高，立体选择性高。此外，还考察了其他还原反应，发现α-二酮的半还原反应、亚砜的脱氧反应等。特别是将后者应用于外消旋膦的动力学拆分，得到旋光性膦。我们发现了几个有用的碳碳键形成反应，还原性官能团的相互转换使用该组合试剂体系。结果表明，该组合试剂体系在有机合成领域具有广阔的应用前景。

We have found that the reduction of α-bromoamide could be achieved under mild conditions using Lewis acid and phosphine combination. Also, it has been already reported that the Reformatsky-type reaction could proceed when the aldehyde was reacted with the intermediate metal enolate, to give the desired β-hydroxyamide in good yield with high stereoselectivity. In this research, we would like to develop the synthetically useful reactions using this methodology.At first, the Reformatsky reaction using α-bromoketones or thioesters, instead of α-bromoadmides, were investigated. As a result, the desired Reformatsky-type products were obtained in good yield with high stereoselectivity by using the combination of titanium tetrachloride and tri-o-tolylphosphine. Next, this reaction was applied to the other electrophile such as thioesters, acetals, and imines. The reaction with thioester have smoothly proceeded to give the reductive-Claisen condensate, and the Mannich-type reaction with imine was also found to give the corresponding adducts in good yield with high stereoselectivity. Moreover, other reductive reactions were also examined and we found the half-reduction of α-diketones, deoxygenation of sulfoxides and so on. Especially, the later was applied to the kinetic resolution of racemic phosphines to give optically active phosphines.We found the several useful carbon-carbon bond forming reactions, reductive functional group interconversions using this combined reagent system. It was found that the combined reagent system was useful in the field of organic synthesis.