Previously unknown 1,2-dihydro-1-aza-2-boraphenanthrene has been synthesized in only three steps from 2-bromo-1-vinylnaphthalene. The reactivity of this new BN-phenanthrene, and of several substituted derivatives, has been tested against bromine and organolithium compounds. Bromination proceeded with complete regioselectivity, affording bromo-substituted compounds suitable for further functionalization via cross-coupling reactions. This new family of BN-phenanthrenes exhibits a substantial increase in the quantum yield (up to ϕF = 0.93) with respect to phenanthrene.
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 the bicyclic core containing a methylenetetrahydrofuran moiety as major product. Several cyclobutane-fused O-heterocycles with diverse substitution are synthesized following the reported methodology.
