10.1002/chem.201000374
The research focuses on the homo-elimination of HF as an efficient approach for intramolecular aryl-aryl coupling, particularly in the synthesis of fullerenes and non-planar polycyclic aromatic hydrocarbons (PAHs). The study explores the use of fluorine as an activating group for promoting ring closure in PAHs through the elimination of HF, a process that was previously thought to be less feasible due to the stability of the C-F bond. Experiments involved the synthesis of 1-fluorobenzo[c]phenanthrene (1) and 2-fluorobenzo[c]phenanthrene (2), which were subjected to flash vacuum pyrolysis (FVP) to observe the selective 1,5 ring closure. The research also included the synthesis and FVP of 1,2,3,4-tetrafluorobenzo[c]phenanthrene (8) to experimentally prove the 1,5-HF elimination. Quantum chemical calculations using DFT with the B3LYP hybrid functional and the 6–311G(d,p) basis set were employed to characterize the potential energy surface for the HF elimination reactions, with activation energies and transition states being key analytical outcomes. The study concluded that fluorine can effectively promote intramolecular condensation, offering a solution to the selectivity problem in FVP and paving the way for efficient conversion of planar PAH precursors to fullerene cages.
10.1016/0040-4039(91)80677-X
The research aims to develop a new method for converting dicarbonyl compounds into alkenes, specifically focusing on the synthesis of phenanthrenes from 2-(2-formylphenyl)benzaldehydes. The study explores various routes to achieve this transformation, including heating the dilithium or disodium salts of the bistosylhydrazones derived from the aldehydes. The researchers initially attempted methods such as the Bacon procedure and titanium coupling but faced challenges, especially with steric hindrance in the synthesis of 4,5-dimethoxyphenanthrene. They then explored the formation of bis-diazoalkanes from bistosylhydrazones, which upon heating, could cyclize to form phenanthrenes. Tosylhydrazine is used as a key reagent to convert the 2-(2-formylphenyl)benzaldehydes into their corresponding bistosylhydrazones. Sodium hydride (NaH) is employed to deprotonate the bistosylhydrazones, forming their sodium salts. The study concludes that this new method is effective for the preparation of sterically hindered phenanthrenes and represents a significant advancement in the field of alkene formation from dicarbonyl compounds.
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