A novel 4‐methylene‐3‐borahomoadamantane: 1,1‐organoboration of an alkyn‐1‐ylsilane using 1‐boraadamantane

1,1‐Dibromo‐2,2‐bis(trimethylsilylethynyl)ethene ( 2 ) reacts with two equivalents of 1‐boraadamantane ( 1 ) by 1,1‐organoboration of both trimethylsilylethynyl groups to give a triene 3 bearing two 4‐methylene‐3‐borahomoadamantane moieties in terminal positions. The triene was characterized by one‐ and two‐dimensional ¹H, ¹¹B, ¹³C and ²⁹Si NMR spectroscopy in solution and X‐ray structural analysis in the solid state. The planes of the C double bond are strongly twisted against each other as a result of the bulky substituents, and the surroundings of the boron atoms deviate from the ideal trigonal planar geometry owing to the tension in the tricyclic frameworks. Copyright © 2006 John Wiley & Sons, Ltd.