Construction of Carbon-Carbon Unsaturated Bond Systems using Transition-Metals

碳-碳不饱和键体系的合成方法因其广泛存在于各种有机化合物中而备受关注。本研究项目关注的是利用过渡金属催化剂开发新型反应，为构建不饱和键体系提供简单有效的途径。共轭烯二炔化合物是重要的，因为它们被认为是一些抗肿瘤药物的关键结构。研究人员发现了一条从丙炔碳酸酯和末端炔开始合成烯二炔的新路线。在钯催化剂存在下，将碳酸丙酯与2摩尔末端炔偶联，得到相应的偶联产物，偶联产物具有共轭烯二炔结构，产率高。该反应在一个锅中一步一步进行，因此，通过连续加成两种不同的炔也可以合成不对称的烯二炔化合物。在研究过程中，研究人员发现，在上述偶联反应中的中间化合物之一——烯基环丙烷，在铑催化剂的作用下，可以通过扩环重排转化为亚甲基环戊烯。这种新的铑催化的烯基环丙烷转化反应，在相当温和的条件下，以选择性的方式得到了具有外环烯烃的共轭二烯化合物，3-亚甲基环戊烯。当取代的烯基环丙烷在阳离子铑配合物的存在下反应时，观察到环丙烷环的高度区域选择性碳-碳键断裂。综上所述，研究者利用过渡金属催化剂建立了两种新的碳-碳不饱和键体系。

Synthetic methodologies for the construction of carbon-carbon unsaturated bond systems have been much attention because of their existence in a wide variety of organic compounds. This research project is concerned with the development of novel types of reactions providing simple, effective routes to construct unsaturated bond systems by using transition metal catalysts.Conjugated enediyne compounds are of importance since they are known as a key structure of some antitumor agents. The investigator found a new synthetic route to enediynes starting from propargylic carbonates and terminal alkynes. In the presence of a palladium catalyst, a propargylic carbonate was coupled with 2 moles of terminal alkynes affording the corresponding coupling products having a conjugated enediyne structure in good yield. The reaction proceeded step by step in one pot, thus an unsymmetrical enediyne compound could be also synthesized by successive addition of two different alkynes.In the course of the study, the investigator found that an allenylcyclopropane, one of the intermediate compounds in the coupling reaction described above, could be transformed into a methylenecyclopentene via a ring-expanding rearrangement, when it was treated with rhodium catalysts. This novel rhodium-catalyzed transformation reaction of allenylcyclopropanes afforded conjugated diene compounds having an exo-cyclic olefin, 3-methylenecyclopentenes, in a selective manner under quite mild conditions. Highly regioselective carbon-carbon bond cleavage of the cyclopropane ring was observed, when substituted allenylcyclopropanes were allowed to react in the presence of cationic rhodium complexes.In summary, the investigator has developed two new reactions constructing carbon-carbon unsaturated bond systems by using transition metal catalysts.