Synthesis of Novel Fused Tropones and Colchicinoids Through Rh(I)-Catalyzed [2+2+2+1] Cycloaddition of Triynes with Carbon Monoxide
Teng, Yu HanGary
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Natural products and their metabolites isolated from diverse natural origins have been an extraordinary starting place for the research of active pharmaceuticals, agrochemicals and other applications. Core structures of those natural products serve as templates to obtain more potent and selective agents through systematic structure-activity relationship (SAR) studies. A unique feature of natural products is that they often contain complex fused-ring skeletons. However, the traditional synthetic methodologies to access these fused-ring skeletons were not efficient in the ease of synthesis and with atom economy. Therefore, the need to develop more efficient synthetic methods that provide access to fused-ring skeletons is essential. Transition metal-catalyzed cycloaddition reactions have proven to be one of the most efficient methods for natural products synthesis as well as constructing natural product-like and drug-like skeletons in highly selective manner as well as with high atom economy. As part of ongoing studies in the Ojima laboratory on the transition metal- catalyzed carbocyclizations and higher-order cycloaddition reactions, the Rh(I)-catalyzed [2+2+2+1] cycloaddition of triynes was investigated. The reaction of triynes in the presence of [Rh(CO)2Cl]2 and CO (2 atm) gave novel 5-7-n fused tricyclic products. In addition, with carefully design of the triyne substrates, novel colchicinoids can be prepared in short steps. The reaction variables as well as the mechanisms for the formation of these fused ring products are presented.