( E , E )‐1,2,3,4‐Tetracyclopropylbuta‐1,3‐diene: Synthesis and Some of Its Properties

( E , E )‐1,2,3,4‐Tetracyclopropylbuta‐1,3‐diene ( 3 ) and (Z,Z)‐1,4‐diodo‐1,2,3,4‐tetracyclopropylbuta‐1,3‐diene ( 4 ) were prepared from dicyclopropylacetylene via an intermediate 2,3,4,5‐tetracyclopropyltitanacyclopentadiene ( 2 ) in 91 and 77 % yield, respectively. In the crystal, 3 adopts a conformation with an almost coplanar (φ = 163°) 1,3‐diene core, with the inner vinylcyclopropane units in an orthogonal and the outer vinylcyclopropane moieties in an s ‐ trans orientation. This diene, like 2,3‐cyclopropylbuta‐1,3‐diene ( 5 ), undergoes facile concerted [4+2] cycloadditions at 130 °C with dimethyl acetylenedicarboxylate as well as N ‐phenylmaleimide and at 0 °C with N ‐phenyltriazolinedione. An X‐ray crystal structure analysis of 2,3‐dicyclopropylbuta‐1,3‐diene ( 5 ) also reveals a coplanar inner core with the vinylcyclopropane units in essentially orthogonal ( φ av = 89.3°) orientation. Differential scanning calorimetry (DSC) measurements indicate that 3 undergoes significant internal reorganization on going from the liquid to the crystalline phase, and a gauche conformer of 3 may well be favored over the s‐trans conformer in the liquid.