Synthesis of a Cyclobutadiene Stabilized by Steric Effects

Abstract

Preparation, properties, and reactions of the new q-cyclopentadienyl(dio1efin)nickel complexes will be reported in detail elsewhere. Tris(v]-methylcyclopentadieny1)dinickel tetrajuoroborate (26)A 50% aqueous solution of HBF, (0.4 ml) is added very slowly with exclusion of air to a solution of (lb) (650 mg, 3 mmol) in propionic anhydride (5 ml). After brief mixing the resulting dark brown solution is carefully added dropwise to vigorously stirred diethyl ether (75 ml). The blackish violet, finely crystalline precipitate is isolated by filtration through a G 3 frit and washed several times with ether. Vacuum drying affords 620 mg of (2b) (93% yield based on (Ib)).

Modeling high pressure reactivity in unsaturated systems: Application to dimethylacetylene

“…As it was noted, there are not experimental data of CBD or TMCBD, but other CBD derivatives have been synthesized and characterized. Experimental data for the tetra-tert-alkylcyclobutadiene [35][36][37] are alike to our results, with a value for the double bond of 1.34 Å , and a distance for the single bond near 1.60 Å .…”

A Diels–Alder super diene breaking benzene into C2H2 and C4H4 units

“…In fact, cyclobutadienes with small substituents are sufficiently reactive to dimerize via a Diels–Alder reaction and can also be trapped with a large variety of dienophiles 3 4 5 . Even isolable cyclobutadienes, with bulky substituents, undergo Diels–Alder cyclization with a variety of reagents 6 7 8 9 . However, aside from the dimerization process, cyclobutadienes almost exclusively react as electron-rich dienes.…”

Ab Initio Study of Cyclobutadieno-p-benzoquinones: Kekulé Isomerization or Not?

“…Antiaromatic cyclobutadiene (CB) belongs, together with its aromatic antipode benzene, to the most exciting organic molecules. Isolation of CB has been a tremendous synthetic challenge for decades because of its extraordinary π-electron antiaromaticity and considerable angular strain. − Brilliant preparative efforts of Pettit, Krebs, Masamune, Meier, Gomper, and others have led to CB transition-metal complexes, CB flanked by large carbocycles, CBs protected by large bulky groups, , and push−pull CBs. , An authoritative review article on the role of CB in the phane chemistry was provided by Gleiter and Merger recently. Each of these systems extends our knowledge and deepens our understanding of the versatile chemical bonding phenomenon.…”