Positron emission tomography (PET) presents an important tool for medicinal and pharmaceutical investigations, with applications ranging from fundamental research to the diagnosis of a broad variety of diseases. Crucial for the use of this technique is, however, a robust labeling strategy for the preparation of the required radiolabeled compound. For 18‐fluorine‐labeling, which represents the most widely applied method in this field, it is interesting to note that a kind of paradigm change occurred over the last years. While multi‐step labeling strategies were the preferred approach for many decades, mainly due to the lack of suitable leaving groups for direct [18F]fluorination reactions, the synthetic tools to achieve the highly attractive direct 18‐fluorine‐labeling rapidly increased recently. This focus review points out a comparison between the multi‐step approaches and the newly developed direct fluorination strategies available for nucleophilic 18‐fluorination of carbocyclic aromatic systems, including a discussion of advantages and limitations.
Substituted indoles can be prepared from phenylazocarboxylates through a rapid one-pot sequence featuring a microwave-assisted Fischer indole synthesis as a key step. Considering that the phenylazocarboxylates may beforehand be modified by mild nucleophilic aromatic substitution, including the introduction of [ F]fluoride, the overall strategy offers an attractive new access to 5-[ F]fluoroindoles.
Low concentrations of nitrogen dioxide, which arises as a side product from a range of industrial processes, can effectively be recycled through the diazotization of anilines. The studies reported herein now demonstrate that the removal of nitrogen dioxide from gas streams is even more effective when hydrophilic anilines are used as starting materials. The diazonium salts, which are obtained in this way in up to quantitative yields, can directly be employed in azo coupling reactions, thus opening up an attractive route to the industrially important group of azo compounds.
From waste to valuables: The industrial production of copper nitrate from copper produces large amounts of toxic NO2. Instead of costly denitrification, this process has now been used for the diazotization of anilines and subsequent synthesis of valuable azo compounds. A wet scrubber plays a key role in this strategy. The studies demonstrate that diazonium salts, obtained from the scrubber in up to quantitative yields, can directly be employed in azo coupling reactions thus opening an attractive access to the industrially important group of azo compounds. More information can be found in the Communication by M. R. Heinrich, et al. on page 4042 ff.
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