Generation of an N→B Ladder-type Structure by Regioselective Hydroboration of an Alkenyl-Functionalized Quaterpyridine.

An unusual reactivity of 2-(1-alkenyl)-pyridines towards hydroboration with 9H-borabicyclo[3.3.1]nonane (9H-BBN) has been employed to selectively introduce two borane groups into a conjugated quaterpyridine. Quantitative conversion of the substrate was observed with exclusive regioselectivity. A molecular structure that allows intramolecular N→B coordination was generated. The effect of the ladder formation on the molecular structure and the electronic properties of the conjugated system have been investigated. The synthetic strategy demonstrated herein offers a facile access to N→B ladder-type structures from readily available substrates, and allows to simultaneously introduce several boron centers under mild conditions.