Fig. 3. Cyclization of linear peptides with isocyanide reagents Pinc and Pinc2. [a] Standard reaction conditions: Pinc (1.2 equiv.), EtCHO (1.5 equiv.) in 1 : 1 MeCN/DCE (25 mM) at 50 °C or Pinc2 (1.5 equiv.), EtCHO (1.5 equiv.), AcOH (0.1 equiv.) in 1 : 1 MeCN/DCE (25 mM) at 50 °C. [b] Cyclic phosphorane 6b observed (see ESI†). [c] Alternative reaction conditions: Pinc (1.5 equiv.), EtCHO (2 equiv.) in 1 : 1 MeCN/DCE (5 mM) at 60 °C or Pinc2 (1.5 equiv.), EtCHO (1.5 equiv.), AcOH (0.1 equiv.) in 1 : 1 MeCN/DCE (5 mM) at 60 °C. [d] After cyclization the peptide was globally deprotected with 3 : 7 TFA/DCM.
