Synthesis of Heterocycles via Electrophilic Cyclization of Alkynes Containing Heteroatom

Synthesis of heterocycles through electrophilic cyclization of alkynes containing heteroatom was reported. These heterocycle rings can be formed through endo or exocyclization modes, depending on the chain length, the substitution pattern on the chain, and the electrophile employed. Starting from 5-substituted Z-enynoic acids 5, the construction of 6-iodopyranones 6 and iodoylidenefuranones 7, in which furanones 6 are the major products, was developed by employing 3 equiv of iodine and 3 equiv of NaHCO3 in CH3CN. The selectivity and the yields of these cyclizations were significantly affected rather by the temperature than the electrophilic sources and nature of these benzoates. Thus, by using 1.0 equiv of ICl as electrophilic source in CH2Cl2, at room temperature, the Z-enynoic acids 5 afforded a 72:28 ratio of lactones 6 and 7. Larock and co-workers subjected a series of acetylenic esters and acids as substrates to the electrophilic cyclization conditions in the preparation of 2(3H)-furanones.