Novel nitrogen-bridged diazocines (triazocines) were synthesized that carry a formyl or an acetyl group at the CH2NR-bridge and bromo- or iodo-substituents at the distant phenyl ring. The photophysical properties were investigated in acetonitrile and water. As compared to previous approaches the yields of the intramolecular azo cyclizations were increased (from ≈40 to 60%) using an oxidative approach starting from the corresponding aniline precursors. The Z→E photoconversion yields in acetonitrile are 80–85% and the thermal half-lives of the metastable E configurations are 31–74 min. Particularly, the high photoconversion yields (≈70%) of the water-soluble diazocines are noteworthy, which makes them promising candidates for applications in photopharmacology. The halogen substituents allow further functionalization via cross-coupling reactions.
Invited for this month's cover is the group of Anna J. McConnell and Christian Näther from Christian‐Albrechts‐Universität zu Kiel, Germany. The cover picture shows an amidoboronate puzzle divided into four quarters that represent four possible amidoboronates. How do these amidoboronates interconvert? The right combination of aniline (yellow circles) and catechol (grey and purple circles) pieces solves this conundrum and the amidoboronates interconvert via dynamic covalent B‐N (left to right) and B‐O bonds (top to bottom). More information can be found in the Research Article by Anna J. McConnell and co‐workers.
Amidoboronates were prepared as a mixture of up to three isomers (rac5, meso5 and rac6) from the reductive coupling of N-aryl iminoboronates with either cobaltocene or decamethylcobaltocene in acetonitrile. The interconversion of rac5 and rac6 isomers via rearrangement of their dynamic covalent B N bonds was investigated in solution by redissolving isolated crystals. The aniline para substituent and catechol within the amidoboronates tuned the distribution between the rac5 and rac6 isomers; the rac6 isomer predominated for amidoboronates based on pyrocatechol with electron-withdrawing substituents and no interconversion was observed for the rac5 isomers of amidoboronates based on tetrachlorocatechol. Furthermore, the rac5/rac6 distribution was altered by catechol exchange of pyrocatechol for tetrachlorocatechol exploiting the dynamic covalent B O bonds.
Diazocines are bridged azobenzenes with phenyl rings connected by a CH2-CH2 group. Despite this rather small structural difference, diazocine exhibits improved properties over azobenzene as a photoswitch and most importantly,...
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