Sequential Formation of Yellow, Red, and Orange 1‐Phenyl‐3,3‐Biphenylene‐Allene Dimers Prior to Blue Tetracene Formation: Helicity Reversal in trans‐3,4‐Diphenyl‐1,2‐bis(fluorenylidene)cyclobutane

Abstract

1-Phenyl-3,3-biphenyleneallene (2), the base-catalyzed rearrangement product of 9-phenylethynylfluorene (1) yields a yellow, head-to-tail dimer 6 that, upon gentle warming, is converted to the red tail-to-tail isomer trans-3,4-diphenyl-1,2-bis(fluorenylidene)cyclobutane (7), in which the two fluorenylidene moieties severely overlap. The helical sense of the fluorenylidene moieties in 7 matches that of the phenyl substituents, and the interplanar angle between the fluorenylidene moieties is 41 degrees . At 80 degrees C, 6 isomerizes to orange cis-3,4-diphenyl-1,2-bis(fluorenylidene)cyclobutane (8), which at 110 degrees C is converted to orange trans diastereomer 9, whereby the helicity of the overlapping fluorenylidene moieties is reversed from that in 7 such that they are aligned with the ring hydrogen atoms, and the interplanar angle between the fluorenylidene moieties is now 60 degrees . At 180 degrees C, 6 rearranges to dispirodihydrotetracene 3 and blue, electroluminescent diindenotetracene 4, which is readily oxidized to peroxide 5. In the solid state, both 3 and 4 adopt structures with Ci symmetry (only an inversion center) such that the central polycyclic framework is nonplanar. Deprotonation of yellow head-to-tail allene dimer 6 with tBuOK in DMSO and reprotonation with HOAc yields the [1,3]-hydrogen migration product 10, in which the proton originally on the cyclobutane ring is now sited at C9 on the exocyclic fluorenyl substituent. Analogously, deprotonation and reprotonation of orange dimer 9 furnishes [1,3]-hydrogen migration product 11. Side product 17, formed during the synthesis of 1 from 9-phenylethynylfluoren-9-ol, BF3 and Et3SiH, was shown to be a silyl-indene spiro-linked to C9 of fluorene. All products were characterized by NMR spectroscopy and X-ray crystallography, and the mechanisms of these interconversions are discussed.

A Synthetic and X‐ray Crystallographic Study of Zinc and Platinum Complexes of 4,5‐Diazafluoren‐9‐one (Dafone) and Dicobalt Hexacarbonyl Derivatives of 9‐Phenylethynyl‐4,5‐Diazafluoren‐9‐ol: Chelation versus Monocoordination

“…As noted above, the conventional route to allenes from alkynols requires treatment with boron trifluoride and triethylsilane to furnish the corresponding alkyne, with subsequent base-promoted isomerisation to the allene; [4][5][6] in the present case, one might suspect that the Lewis acidic BF 3 would preferentially bind to a ring nitrogen atom and so preclude this approach. An alternative approach (Scheme 1) involves the reaction of the alkynol with cold dilute HBr to yield a bromoallene that can be lithiated and then quenched with water or dilute acid.…”

“…[1][2][3] As depicted in Scheme 1, treatment of fluorenone with an alkynyllithium yields the corresponding 9-alkynylfluoren-9-ol, 1. Conversion to the required 3,3-(biphenyl-2,2Ј-diyl)-1-arylallene 3 can be accomplished either by reaction with BF 3 /Et 3 SiH (to form an alkyne 2, which readily rearranges under basic conditions) [4][5][6] or by formation of the bromoallene 4, [7] followed by lithiation and hydrolysis.…”

Exploiting [2+2] cycloaddition chemistry: achievements with allenes

“…35 Reaction of 9-ethynyl-9H-fluoren-9-ol 92a with dilute aqueous HBr at 0 1C to room temperature for 5 h gave the corresponding cyclobutane 91a in 85%. On the other hand, reaction of 9-phenylethynylfluorene 92b with triethylamine at 0 1C to room temperature overnight provided the [2+2] head-to-tail dimer 91b.…”

From Allenes to Tetracenes: A Synthetic and Structural Study of Silyl‐ and Halo‐Allenes and Their Dimers

“…In continuation of our studies on the syntheses and dimerizations of fluorenylidene-derived allenes to form bis-(alkylidene)cyclobutanes, and ultimately tetracenes, [1][2][3] we wished to incorporate substituents containing other main group elements, in particular silicon and/or halogens. Since many tetracenes are known to be electroluminescent, [4] it was hoped that the introduction of a wider range of functional groups into the precursor allenes would allow greater control of their luminescent and other photophysical or electro-conductive properties.…”