Synthesis of base-free boriranes and their conversion to borirenes using strong reductant†

Boriranes, highly strained three-membered cyclic organoboron heterocycles, have emerged as potential synthons for the synthesis of many organoboron species. However, the synthesis of boriranes with tricoordinate, sp²-hybridised boron and tetracoordinate, sp³-hybridised carbon atoms is very challenging owing to their high Lewis acidity. Herein we describe the isolation of base-free triaminoboriranes from the room-temperature reaction of diaminoalkynes with an aminodistannylborane. Further elimination of stannyl groups from these boriranes using potassium graphite afforded 2π-aromatic triaminoborirenes. To our knowledge, these are the first examples of conversions of alkanes to alkenes using reducing agents. Interestingly, the triaminoborirene underwent photolytic ring opening to afford a boryl- and amino-substituted acetylene featuring a polarised alkynyl group.