C1-alkynylation of tetrahydroisoquinoline by A³ reaction using metal-organic framework Cu₂(BPDC)₂(BPY) as an efficient heterogeneous catalyst

Abstract

A metal-organic framework Cu₂(BPDC)₂(BPY) was synthesized and used as a heterogeneous catalyst for the copper-catalyzed A³ reaction of tetrahydroisoquinoline, aldehydes, and alkynes to form C1-alkynylated tetrahydroisoquinolines. High regioselectivity to the endo-yneproduct was achieved, with more than 99% of 2-benzyl-1-(phenylethynyl)-1,2,3,4-tetrahydroisoquinoline and less than 1% of 2-(1,3-diphenylprop-2-ynyl)-1,2,3,4-tetrahydroisoquinoline being observed in the product mixture. The Cu₂(BPDC)₂(BPY) also exhibited higher catalytic activity for the transformation than that of other Cu-MOFs such as Cu(BDC), Cu₂(BDC)₂(BPY), Cu₂(EDB)₂(BPY), Cu₃(BTC)₂ and Cu₂(BDC)₂(DABCO). No product was detected for the reaction using other MOFs including Mn(BDC), Co-MOF-74, Zn-IRMOF-61, and Ni₂(BDC)₂(DABCO). The Cu₂(BPDC)₂(BPY) catalyst could be recovered and reused several times without a significant degradation in catalytic activity.