Exploring the reactivity of 9-phenyl-9-borafluorene with 1,2-dipolar molecules.


The reactions of 9-phenyl-9-borafluorene with 1,2 dipolar molecules, specifically carbonyls, and protic substrates, were investigated. With respect to carbonyls, an aldehyde, ketone, and ketene all demonstrated insertion into the endocyclic B-C bond to furnish a BOC5 heterocycle. These reactions proved the ability of 9-borafluorenes to react with 1,2 dipolar reagents to generate 7-membered boracycles with a biphenyl backbone. The relative stability and reactivity of 9-phenyl-9-borafluorene was probed by it's reactivity with N-H, O-H, S-H, and P-H bonds. Protodeborylation was observed for phenol, water, aniline, and 4-bromothiophenol. In the case of water, both O-H bonds reacted with two units of 9-phenyl-9-borafluorene to furnish the oxygen bridged diborane, wheras only a single N-H bond of aniline reacted. Phenylphosphine coordinated to the boron center to give an adduct that did not react further. The reactivity was compared to reactivity with pentaphenylborole.



Borafluorene. Ring insertion. Ring opening. Boron. Anti-aromatic. Borole.