Chain extension reactions of acetylenes. Part 2. A comparison of the reactions of butyl-lithium with 1-iodoalk-1-ynes and 1-bromoalk-1-ynes

Abstract

1-lodohept-1-yne reacts with 2 equiv. of butyl-lithium to form octane and hept-1-yne, whereas 1-bromohept-1-yne undergoes butylation at C-3. In the presence of 1 equiv. of butyl-lithium, metal–halogen exchange gives butyl iodide and lithium hept-1-ynide, which couple to form undec-5-yne on addition of hexamethylphosphoric triamide. The reaction of 2 equiv. of butyl-lithium with either 1-bromo- or 1-iodo-propyne gives largely octane, but chain extension of 1-bromopropyne occurs to give hept-1-yne when 3 equiv. of butyl-lithium are used and butyl bromide is then added. Addition of iodine after butyl bromide gives 1-iodohept-1-yne.