4′-Ethynylbenzo-12-crown-4 (8), 4′-ethynylbenzo-15-crown-5 (9), and 4′-ethynylbenzo-18-crown-6 (10) were synthesized by cross-coupling of the corresponding aryl iodides 1-3 with 2-methylbut-3-yn-2-ol (4a) followed by the retro-Favorsky cleavage of the resulting carbinols. Unlike the corresponding benzo-12-crown-4 derivative (5a), the cleavage of tertiary acetylenic alcohols of benzo-15-crown-5 (6a) and benzo-18-crown-6 (7a) requires more than one molar equivalent of KOH. Aminoalkylation of crown ether 8 gives Mannich bases, independently of the reaction conditions and the nature of amine. The aminomethylation of acetylenic crown ethers 9 and 10 with paraform-piperidine (morpholine) in the presence of CuCl yields 1,4-disubstituted buta-1,3-diynes (19, 20) rather than Mannich bases.
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