Synthesis of polyether cyclophanes through rhodium-catalyzed cross-alkyne cyclotrimerization

Cross-cyclotrimerizations of ether-linked alpha,omega-diynes and dimethyl acetylenedicarboxylate in the presence of a catalytic amount of cationic rhodium(I)/H-8-BINAP complex give [7][21]polyether cyclophanes in good yield. [8]-[9]Ester cyclophanes were also synthesized from the corresponding alpha,omega-diynes. The ratio of para-, meta-, and orthocyclophanes depends on the length and the structure of the alpha,omega-diyne tether chain, whilst the effect of concentration on the yield of polyether cyclophanes appears to be small. X-ray analysis revealed that a single crystal of 115]metacyclophane 4g was the chiral form and that of [5.5]metacyclophane 4k the racemic form, due to an absence of ring flip in the crystals. (c) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006.