Science of Synthesis

Iyoda, M., Science of Synthesis, (2010) 45, 542.

Expanded radialenes is the general term given to the cyclic compounds constructed by formal insertion of unsaturated spacers between exocyclic radial double bonds as shown in ‌Scheme 55‌. Expanded radialenes ‌182‌–‌184‌ with acetylene spacers, diyne spacers, and π-spacers are typical examples. The synthesis of expanded radialene ‌183‌ by the insertion of a diyne moiety into the radialene framework has been reported,[‌12‌] and it has been extended to a number of molecules having acetylene spacers, π-spacers, and heteroatom spacers.[‌3‌] Although a variety of synthetic methods have been developed for constructing radialene frameworks (see Sections ‌45.12.1‌–‌45.12.4‌), rather limited procedures have been employed for the synthesis of expanded radialenes based on cross- and homocouplings of alkynes.[‌140‌] The syntheses of cyclic conjugated diynes, triynes, tetraynes, and polyynes are summarized in Science of Synthesis, Vol. 43 [Polyynes, Arynes, Enynes, and Alkynes (Section ‌43.2‌43.2)], and some cross couplings and homocouplings of acetylenes are described there. Methods for the synthesis of expanded radialenes are therefore not covered in this section.

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References