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多种有机化合物中而备受关注。本研究项目致力于开发利用过渡金属催化剂构建不饱和键体系的简单、有效途径的新型反应。共轭二炔化合物是一些抗肿瘤药物的关键结构，具有重要意义。这位研究人员发现了一条从炔丙基碳酸酯和末端炔烃开始合成烯二炔的新路线。在钯催化剂存在下，丙烯酸碳酸酯与2个摩尔末端炔发生偶联反应，得到具有共轭二炔结构的偶联产物。该反应在一锅中逐步进行，两种不同的烯烃相继相加也可合成不对称的烯二炔化合物。在研究过程中，研究人员发现，上述偶联反应中的中间化合物之一的烯丙基环丙烷，经扩环重排反应后，可以通过扩环重排转化为亚甲基环戊烯。这种新颖的Rh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和3-亚甲基环戊烯的共轭二烯化合物。当取代的烯丙基环丙烷在阳离子Rh络合物存在下反应时，观察到环丙烷环的高区域选择性的碳-碳键断裂。综上所述，研究人员利用过渡金属催化剂开发了两个构建碳-碳不饱和键体系的新反应。

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.