Chemo- and regioselective intermolecular cyclotrimerization of terminal alkynes catalyzed by cationic rhodium(I)/modified BINAP complexes: Application to one-step synthesis of paracyclophanes

A highly regioselective intermolecular cyclotrimerization of terminal alkynes has been developed based on the use of the cationic rhodium(i)/ DTBM-Segpbos 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-cyclotfimerization 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 alpha,omega-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.