Synthesis of Phenacene-Helicene Hybrids by Directed Remote Metalation

Abstract

Polycyclic aromatic hydrocarbons (PAHs) with six and seven rings were synthesized via directed metalation and cross-coupling of chrysenyl N,N-diethyl carboxamides with o-tolyl and methylnaphthalenyl derivatives. In the presence of competing ortho sites, the site selectivity in iodination of chrysenyl amides by directed ortho metalation (DoM) was influenced by the lithium base. The catalyst ligand bite angle was presumably important in the cross-coupling of sterically hindered bulky PAHs. Subsequent directed remote metalation of biaryls under standard conditions and at elevated temperatures afforded various fused six- and seven-ring PAHs, all in good yields and with fluorescent properties.

Scheme 1. Synthesis of Phenanthrenes by Directed Metalation and Cross-Coupling Strategies

Scheme 2. DreM Resulting in Different Products Depending on the Connecting Position of the Naphthyl Group. Examples (a,b) by Fu, et al.(59) and Example (c) by Lorentzen, et al.(63)

Scheme 3. Electrophilic Substitution of N,N-Diethylchrysenecarboxamides by DoM

Scheme 4. Preparation of Methylnaphthalenyl Boron Pinacolate Cross-Coupling Partners

Figure 1

Ligand bite angle (β°) for selected catalysts: PdCl₂(dppf), PdCl₂(dppp),^, PdCl₂(dppe),^, and PdCl₂(dppm)

Scheme 5. ISQ Experiments on Selected Substrates

Scheme 6. Reinvestigated Synthesis of 6ib

Figure 2

Plots showing UV–vis absorption and fluorescence spectra of PAHs dissolved in CHCl₃ with normalized intensity on the y-axis and wavelengths in nanometer on the x-axis.