Silyl-cupration of an acetylene followed by ring-formation

The acetylenes 1a-e undergo silyl-cupration followed by cyclisation, the ac etylenes 1f-1h react with the silyl-cuprate reagent more rapidly at the alt ernative electrophilic site, and the acetylenes 1i, 1j and 17 give relative ly low yields of cyclic products amongst others. Ring-formation is, unusual ly, a not particularly favourable pathway.