The limited supplies of biologically active natural products from natural source have been a severe bottleneck for their application to medical care or mechanistic study of their functions. Synthetic organic chemistry may become a best possible solution of this supply problem by the development of practical synthetic methods suited to the intended molecules. For right-half of halichondrin B, we established a new catalytic cycle of Cr-mediated coupling reaction, new asymmetric Ni/Cr-mediated coupling reaction, surprisingly efficient catalytic Cr-mediated coupling reaction, catalytic Ni/Cr-mediated macrocyclization without use of high-dilution techniques, and effective device for forming polycyclic ring system of halichondrin B. For mugineic acid, we established the practical synthesis of 2'-deoxy mugineic acid with minimal requirements for workup and purification procedure, efficient synthesis of mugineic acid, and synthesis of mugineic acid derivatives as molecular probes. For E-ring of palau'amine, we established Hg(OTf)₂-catalyzed olefin cyclization reactions, and its application to the construction of tetra-substituted carbon center possessing nitrogen that corresponds to C16 position of palau'amine.