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

Abstract

(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 (φav = 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.