Methylenierung von [2.2]Paracyclophan‐1,9‐dien und [2.2]Paracyclophan

Abstract

[2.2]Paracyclophan reagiert mit Diazomethan in Gegenwart katalytischer Mengen von CuCl unter Bildung eines stabilen Derivates des cis‐Bishomobenzols (1) und unter Aufweitung eines Benzolringes (2). Daneben entstehen weitere Produkte ähnlicher Art.

Heats of Formation of [2.2]Paracyclophane-1-ene and [2.2]Paracyclophane-1,9-diene − An Experimental Study

“…In conclusion, the increased strain energies (by 4.6 and 11.9 kcal mol -1 ) of 2 and 3 over 1 correlate with the structural changes (Figure ) and also with the observed increased reactivities in cycloaddition reactions . It is noteworthy that the activation enthalpy Δ H ⧧ for the homolytic cleavage of the C,C-single bond in 1 (37.7 kcal mol -1 ) is only 7.6 kcal mol -1 higher than its strain energy (30.1 kcal mol -1 ), and for 2 (Δ H ⧧ = 34.4 kcal mol -1 ) 24 it is virtually the same as the SE (34.7 kcal mol -1 ).…”

“…[2.2]Paracyclophane ( 1 ), first prepared by Farthing in 1949 and in the following 20 years thoroughly investigated by Cram et al, has become the archetype of strained compounds with bent aromatic rings . The [2.2]paracyclophane-1-ene ( 2 ) and the [2.2]paracyclophane-1,9-diene ( 3 ) have to be strained to the same or an even higher extent, as the bending angle of the benzene moieties increases upon introduction of one or two double bonds into the bridges. , Consequently, the reactivity of the benzene rings in 2 and 3 toward cycloadditions of electrophilic reagents increases in the order 1 < 2 < 3 . To quantify the additional strain in 2 and 3 , we have determined heats of formation, Δ (g), of both compounds by high precision combustion calorimetry and the transpiration method, using carefully purified samples (>99.98% pure form).…”

[1:2,9:10]Bismethano[2.2]paracyclophane

“…Previous attempts to prepare such a system by cyclopropanation of [2.2] paracyclophane-1,4-diene with diazomethane were unsuccessful. 4 This reaction leads to preferential attack on the aromatic double bonds and yields products similar to those observed from the reaction of diazomethane with other [2.2] paracyclophane derivatives. 4-"' In the preparation of [2.2.2](1,2,4)cyclophane, it was demonstrated that carbon-carbon bond formation via transannular reductive dehalogenation was an effective and efficient means of introducing additional bridges (and additional ring strain) into cycles which already contained benzene rings in a face-to-face configuration.6 A simple extension of this procedure was used in an attempt to synthesize [ 1:2,9:10]bismethano[2.2]paracyclophane (I) through a double ring contraction of [3.3]paracyclophane.…”

Partially Hydrogenated [2.2]Paracyclophanes as Precursors in Polycyclic Hydrocarbon Chemistry

“…Both cyclopropanation and epoxidation of [2.2]paracyclophanes are welldocumented processes, [11] and examples are even known where the benzene rings are attacked preferentially over double bonds in methylenations of paracyclophanes. [12] In a final competition experiment with 3, the addition of dehydrobenzene (8), the double bond was again the exclusive point of attack, yielding the phenyl-substituted hydrocarbon 9, albeit in poor yield. The structure of 9, formed most probably by an ene-reaction of 3, was proved by extensive NMR studies, including NOE, C,H-correlation, and H,H-COSY experiments (see Exp.…”