Cyclic Diaryl λ-Bromanes as a Precursor for Regiodivergent Alkynylation Reactions.

Regiodivergent reactions are a fascinating tool to rapidly access molecular diversity while using identical coupling partners. We have developed a new approach for regiodivergent synthesis using the dual character of hypervalent bromines. In addition to the recently reported reactivity of hypervalent bromines as aryne precursors, the first transition metal-catalyzed reaction is reported.

Regioselective trans-Hydrostannation of Boron-Capped Alkynes.

Alkynyl-B(aam) (aam=anthranilamidato) derivatives are readily available bench-stable compounds that undergo remarkably selective reactions with Bu SnH in the presence of [Cp*RuCl] as the catalyst. The addition follows a stereochemically unorthodox trans-selective course; in terms of regioselectivity, the Bu Sn- unit is delivered with high fidelity to the C-atom of the triple bond adjacent to the boracyclic head group ("alpha,trans-addition"). This outcome is deemed to reflect a hydrogen bonding interaction between the protic -NH groups of the benzo-1,3,2-diazaborininone ring system and the polarized [Ru-Cl] bond in the loaded catalyst, which locks the substrate in place in a favorable orientation relative to the incoming reagent.

Rhodium(III)-Catalyzed C(sp)-H Functionalization of Cyclobutenes. Access to Cyclobuta[]pyridones and -pyridines.

-(ω-Alkynyl) hydroxamates derived from cyclobutenyl carboxylic acids were identified as viable substrates in intramolecular rhodium(III)-catalyzed heteroannulations, which led to diversely substituted cyclobuta[]pyridones. Further functionalization of the resulting cyclobutapyridones enabled the synthesis of cyclobuta[]pyridines and other nitrogen heterocycles after electrocyclic ring opening of the four-membered ring.