Functionalized Alkynyllithium Compounds

As previously commented for other acetylenic anions, functionalized alkynyllithium compounds of the type XXK were prepared almost exclusively by deprotonation of the corresponding terminal alkynes. Thus, the dihydropyran derivative 217 has been used for the convergent synthesis of trans-fused polytetrahydropyr-ans, which are present in marine toxins by coupling with triflates [180]. 

A different strategy towards <5-functionalized alkynyllithium compounds consists in the treatment of gem-dibromoaDcenes (accessible from the corresponding aldehydes) with an excess of -BuLi. Following this methodology, intermediate 219 was prepared from the dithiane derivative 218 and alkylated with methyl iodide to give the corresponding alkyne 220 (Scheme 2.29) [181]. 

Molander has reported the synthesis of functionalized alkynyl trifluoroborates by transmetallation of alkynyllithium compounds with boronates followed by in situ treatment with KHFjIlll]. These alkynyl trifluoroborates are crystalline solids possessing excellent air stability and are shown to undergo facile cross-coupling for example with 4-bromobenzonitrile to give functionalized arylacetylenes in high yields. Thus, the reaction is tolerant to a variety of sensitive functional... 

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