Cycloisomerization of Alkynyl Ketones to Multisubstituted Furans

Significance

An efficient synthesis of tri- and ­tetrasubstituted furans and indolizines via cyclo­isomerization of alkynyl ketones and pyridines is reported. ¹⁷O-labeling experiments (as shown) were employed to demonstrate plausible mechanisms, which indicate that, for the substrates of conjugated alkynyl ketones and alkynyl pyridines, the cycloisomerization proceeds via 1,3-phosphatyloxy migration to A or 1,2-acyloxy migration to B, respectively. For the skipped alkynyl ketone substrates C, other reaction routes were suggested.