Abstract
A highly regioselective intermolecular cyclotrimerization of terminal alkynes has been developed based on the use of the cationic rhodium(I)/DTBM‐Segphos complex. This method can be applied to a variety of terminal alkynes to provide 1,2,4‐trisubstituted benzenes in high yield and with high regioselectivity. A chemo‐ and regioselective intermolecular crossed‐cyclotrimerization of dialkyl acetylenedicarboxylates with a variety of terminal alkynes has also been developed based on the use of the cationic rhodium(I)/H8‐BINAP complex, furnishing 3,6‐disubstituted phthalates in high yields. It constitutes a highly efficient new method for intermolecular crossed‐cyclotrimerization of two different monoynes in terms of catalytic activity, chemo‐ and regioselectivity, scope of substrates, and ease of operation. The versatility of this new crossed‐alkyne cyclotrimerization procedure is demonstrated through its application to one‐step synthesis of a [6]metacyclophane and [7]–[12]paracyclophanes from the corresponding terminal α,ω‐diynes. Mechanistic studies have revealed that the chemo‐ and regioselectivity of this crossed‐alkyne cyclotrimerization are determined by the preferential formation of a specific rhodium metallacycle derived from a terminal alkyne and a dialkyl acetylenedicarboxylate.