Which isomer is it, 1,2,5,6- or 1,4,5,8-tetrasubstituted cycloocta-1,3,5,7-tetraene? Synthesis of symmetrically tetrasubstituted cycloocta-1,3,5,7-tetraene derivatives.

Ni(0) catalyzed cyclotetramerization [(2 + 2 + 2 + 2) cycloaddition] of propargyl alcohol gave D2 symmetric 1,4,5,8-tetrakis(hydroxymethyl)cycloocta-1,3,5,7-tetraene (1) as the major product contrary to what was reported earlier to be the corresponding C2v symmetric isomer, namely 1,2,5,6-tetrakis(hydroxymethyl)cycloocta-1,3,5,7-tetraene. The structure of 1 has been unambiguously assigned on the basis of single crystal XRD data which showed a very interesting "densely" intermolecularly hydrogen bonded solid state supramolecular structure. Tetrabromide (3) prepared from tetra-alcohol (1) reacted with a variety of nucleophiles, namely carbon, nitrogen, sulfur and phosphorus nucleophiles, to give the corresponding derivatives in good yields. The tetraphosphonate derivative (9) underwent the Wittig-Horner reaction with aromatic aldehydes to give the corresponding tetra-styryl derivatives (10a-i). The reaction of tetrabromide with aniline, benzyl amine and R(+)-α-methylbenzyl amine gave the corresponding C2v symmetric pyrroline fused 1,2,5,6-tetra-substituted cycloocta-1,3,5,7-tetraene derivatives, while all the other derivatives belonged to D2 symmetric 1,4,5,8-tetra-substituted cycloocta-1,3,5,7-tetraene. Quantum mechanical calculations support the above conclusion based on the relative stabilities of the two isomers. The fusion of a 5-membered pyrroline ring with the tub-shaped cyclooctatetraene (COT) ring leads to flattening of the tub (shallow tub) making it easier for the ring inversion of COT through a planar intermediate to take place readily resulting in the formation of C2v symmetric pyrroline fused COT derivatives.

Synthesis and application of 3,4,7,8-tetrakis-exo-methylenecycloocta-1,5-diene as a versatile Diels-Alder diene: synthesis of V-shaped cyclooctatetraene fused acenes.

V-shaped molecules with a cyclooctatetraene (COT) core and rigid acene wings are an interesting class of compounds from the point of view of synthetic challenge and their applications in various fields such as photonics and molecular electronics. A new Diels-Alder diene, namely 3,4,7,8-tetrakis-exo-methylenecycloocta-1,5-diene (1), has been synthesized on a multigram scale by the debromination of 1,4,5,8-tetrakis-bromomethylcycloocta-1,3,5,7-tetraene (2) using either zinc powder or NaI. Compound 1 was used as a Diels-Alder diene with various dienophiles to yield the corresponding double Diels-Alder adducts. The Diels-Alder adducts have a COT core and dihydroaromatic wings which were aromatized with a variety of reagents. The methodology described herein provides a direct and shorter route for the synthesis of COT fused with rigid aromatic wings (V-shaped) compared to the existing iterative multistep synthesis of such compounds.