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.