Regiodivergent Electrophilic Cyclizations of Alkynylcyclobutanes for the Synthesis of Cyclobutane-Fused O-Heterocycles.

Cyclobutane-fused dihydropyrans and methylenetetrahydrofurans are highly interesting cores found in numerous natural products. Both these cores are selectively prepared from a common alkynylcyclobutane precursor bearing an appended hydroxyl group herein. Thus, cyclobutane-fused dihydropyrans can be obtained by a selective 6-endo-dig iodocyclization, whereas gold-catalyzed 5-exo-dig cycloisomerization provides a bicyclic core containing a methylenetetrahydrofuran moiety as major product. Several cyclobutane-fused O-heterocycles with diverse substituents are synthesized following the reported methodology.