A new, effective catalytic system based on Co(acac) has been developed for [6 + 2] cycloaddition of terminal alkynes to 1,3,5,7-cyclooctatetraene to give substituted bicyclo[4.2.2]deca-2,4,7,9-tetraenes in high yields (68-85%). The electrophilic activation of double bonds in the bicyclic products with m-CPBA is an efficient method for the synthesis of substituted bicyclo[4.3.1]deca-2,4,8-triene-7,10-diols, which form the key structural moieties of numerous natural biologically active compounds. The structures of the obtained compounds were reliably proven by modern spectral methods and X-ray diffraction. The mechanism of the discovered rearrangement was studied both using deuterium-labeled bicyclo[4.2.2]deca-2,4,7,9-tetraenes and utilizing quantum chemical calculations. The obtained substituted bicyclo[4.3.1]deca-2,4,8-triene-7,10-diols and their keto derivatives showed high antitumor activity in vitro against Hek293, Jurkat, K562, and A549 tumor cell lines.

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The [6π+2π]‐cycloaddition of O‐, S‐, N‐, Hal‐, and Si‐containing alkynes and 1,3‐diynes to 1,3,5,7‐cyclooctatetraene was accomplished for the first time using a Co(acac)2‐based four‐component catalytic system [Co(acac)2/dppe/Zn/ZnI2] to give previously undescribed functionally substituted bicyclo[4.2.2]deca‐2,4,7,9‐tetraenes in 72–95% yields. These products are of interest as key monomers for the synthesis of natural and synthetic biologically active compounds.

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