Cyclobutene formation in PtCl2-catalyzed cycloisomerizations of heteroatom-tethered 1,6-enynes.

Aza(oxa)bicyclo[3.2.0]heptenes are accessed through the PtCl2 -catalyzed cycloisomerizations of heteroatom-tethered 1,6-enynes featuring a terminal alkyne and amide as the solvent. It is shown that the weak coordinating properties of the solvent and alkyl substituent(s) at the propargylic carbon atom favor the formation of cyclobutenes instead of other possible cycloisomerization products such as 1,3-diene derivatives or cyclopropane-fused heterocycles.