Scheme 2. Synthesis of Symmetric and Asymmetric Bis-ONDs, and Structures of Tris- and Tetra-ONDs.

Reagents and conditions: (a) 1 equiv of furfurylamine, 1.4 equiv of DCC, CH₂Cl₂, 6 h; (b) 1.3 equiv of ethyl 4,4,4-trifluoro-2-butynoate, toluene, 60 °C, 40 h.