4Mracf Ethyl 3-iodo-4,4,4-trifluoro-2(Z)-butenoate (2) was regio-and stereospecific prepared horn ethyl 4,4,4-trifluoro-2-bu@ote (l). The Sonogashira reaction of 2 with terminal alkynes afforded the (2Z)-en-4-ynoic acid derivatives containing triflUOrOMethyl grOUp(4). @ 1997Elsevier ScienceLtd.
Trifluoromethylated organic molecules often confer significant changes in their chemical and physical properties, and therefore methods for the synthesis of trifluoromethylated compounds received a growing interest in recent years. 1 Trifluoromethylation2 and halogen-exchange reaction3 are possible methods for constructing trifluoromethylated compounds, but these suffer from low reactivity and low selectivity. An alternative approach is the preparation and application of trifluoromethylated building blocka.4 We described herein the regio-and stereo-specific preparation of ethyl 3-iodo-4,4,4-trifluoro-2(z)-butenoate (2) , a novel trifluoromethylated building block, and its application as a partner in the Sonogashira reaction.
Several years ago, Lu et. al 5 reported the nucleophilic hydrohalogemtion of 2-alkynoic acids by heating with lithium halides in HOAC. Based on Lu's procedure, We were delighted to observe that the reaction of 1 with sodium iodide in acetic acid afforded 2 as sole product in 7fr~0 isolated yield (eq. 1).6Although the trifluoromethyl group possesses powerfid electron-withdrawing ability,' the iodide ion attacks at the ~position of the carbonyl group and the resulting reaction implied that trifluoromethyl group plays no role in nucleophilic hydrohalogenation of 1. Because compound 1 is highly volatile, the reaction was carried out in a sealed tube. The starting material 1 was easily prepared tiom ct-acylmethylenephosphorane.8 This method