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This review is devoted to the analysis of works published over the past 20 years on the chemistry of saturated annulated nitrogen-containing polycyclic compounds, the molecules of which consist of four, five, six, and seven cycles, and contain from one to eight endocyclic nitrogen atoms.

Spirothiopyran (STP) is particularly attractive when used as a mechanophore to endow polymers with both damage-signaling and self-reinforcing capacity. It is, however, not clear the actual force required to induce the cycloreversion of STP into ring-opened thiomerocyanine (TMC), which reacts spontaneously with activated C-C bonds. Here, we used atomic force microscopy (AFM)-based single molecule force spectroscopy (SMFS) to study the mechanochemistry of STP mechanophore. It is found that the ring-opening of STP at room temperature requires forces of ∼ 200–400 pN, depending on the pulling speed. In addition, the reversibility of STP to TMC isomerization is demonstrated. Finally, mechanochemically induced intermolecular Click addition is achieved in single molecule level by pulling STP in the presence of maleimide.

Triazatriangulenium (TATA) and trioxatriangulenium (TOTA) ions are particularly suited systems to mount functional molecules onto atomically flat surfaces such as Au(111). The TATA and TOTA units serve as platforms that absorb onto the surface and form ordered monolayers, while the functional groups are protruding upright and freestanding from the central carbon atoms. Azobenzene derivatized TATA’s are known to exhibit extremely fast cis → trans isomerization on metal surfaces, via a peculiar non-adiabatic singlet→triplet→singlet mechanism. We now prepared norbornadienes (NBD) and quadricyclanes (QC) attached to TATA and TOTA platforms which can be used to check if these accelerated rates and the spin change mechanism also apply to [2 + 2] cycloreversions (QC→NBD).

The chemical reactivity of the first- and second-generation Grubbs catalysts has always been a significant issue in olefin metathesis. In the present work, we study the [2+2] cycloreversion/cycloaddition and the alkylidene rotation involved into the interconversion of the ruthenacyclobutane intermediate, through the reaction force and reaction force constant analysis. It has been found that the structural contribution controls the barrier energy in the interconversion of ruthenacyclobutane via [2+2] cycloreversion/cycloaddition, which is slightly lower in the second generation of Grubbs catalysts while its electronic contribution is slightly higher, which unveils a major rigidity and donor/acceptor properties of the NHC. This finding explains a greater structural contribution in the rate constant. Moreover, on the basis of the reaction force constant, the process can be classified as “two-stage”-concerted reactions, noting a more asynchronous process when the first generation is used as a catalyst. Finally, a similar analysis into the alkylidene rotation was performed. It was determined that [2+2] cycloreversion and alkylidene rotations take place in a sequential manner, the energy barrier is again controlled by structural reorganization, and the pathway is less asynchronous.

α,ω‐Bis(1,8‐dichloroanthracen‐10‐yl)alkanes with (CH2)n‐linker units (n=1–4) were synthesized starting from 1,8‐dichloroanthracen‐10(9H)‐one. This was transformed into anthracenes with allyl, bromomethyl and propargyl substituents in position 10; these were converted in various C−C‐bond formation reactions (plus hydrogenation), leading to two anthracene units flexibly linked by α,ω‐alkandiyl groups. 1,2‐Ethandiyl‐ and 1,3‐propandiyl‐linked derivatives were functionalized with ethynyl groups in positions 1, 8, 1’ and 8’, and these terminally functionalized by Me3Sn groups using Me2NSnMe3. All linked bisanthracenes were subjected to UV light induced cyclomerization and a series of 9,10 : 9’,10’‐photo‐cyclomers were obtained. Their thermal cycloreversion and (repeated) switchability was demonstrated. 1,3‐Bis1,8‐bis[(trimethylstannyl)ethynyl]anthracen‐10‐ylpropane served as model compound for photo‐switchable acceptor molecules and its open and closed forms were characterized by NMR and DOSY experiments. Light on the switch: Linked bisanthracenes bearing four (partly metal‐containing) substituents undergo photo‐cyclomerization that enables the parallelization of all four functions and can be thermally reopened by cycloreversion which allows repeated switchability.

We report a theoretical study of the thermal decomposition of benzene endoperoxide. A comparison between unrestricted density functional theory (UDFT) and highly correlated multireference ab initio methods has been carried out in order to assess the accuracy and reliability of UDFT to describe biradical mechanisms. The conclusion is that UDFT is a promising tool to describe the biradical mechanisms of endoperoxides. However, it can fail in the particular case of high multiconfigurational character associated with a rather weak biradical character, which happens in the first step of the stepwise cycloreversion mechanism of the prototype system studied, depending on the exchange–correlation functional used. Thus, caution has to be taken when arguing about the possible non-existence of biradical pathways with UDFT.

This chapter contains sections titled: Introduction Maleimide Functional Group Containing Polymeric Materials The Diels‐Alder/Retro Diels‐Alder Cycloaddition‐Cycloreversion Reactions Application of Diels‐Alder/Retro Diels‐Alder Reaction to Synthesize Maleimide‐Containing Polymers Conclusions References

This chapter contains sections titled: Introduction Cycloadditions Sigmatropic Rearrangements Electrocyclizations Mixed Transformations Concluding Remarks References

The strategy employing the cycloreversion reaction in the final step is a very powerful method for the preparation of highly conjugated compounds, which are so far unknown, difficult to access, intractable to purify, or impossible to measure. In this chapter, successful examples of such retro‐Diels‐Alder (rDA) approaches as well as the cheletropic cycloreversion are discussed by sorting the types of targeted large π‐systems. Topics discussed include π‐system expansion of porphyrinoids, π‐expansion of porphyrazines and phthalocyanines, π‐fusion of porphyrin oligomers, π‐fusion of porphyrin and polycyclic aromatic hydrocarbons, π‐expansion and fusion of boron‐dipyrromethenes (BODIPYs), π‐expansion of miscellaneous compounds based on bicyclo[2.2.2]octadiene (BCOD)‐fused pyrroles, and π‐system construction of acenes.