Iterative arylation of itaconimides with diazonium salts through electrophilic Palladium catalysis : divergent β-H-elimination pathways in repetitive Matsuda-Heck reactions

N-Arylitaconimides, accessible from maleic anhydride, anilines and paraformaldehyde, react with arene diazonium salts in a Pd-catalyzed Matsuda-Heck arylation to the pharmacologically relevant E-configured 3-arylmethylidene pyrrolidine-2,5-diones (also known as arylmethylidene succinimides) through an exo-selective β-H-elimination. The coupling proceeds at ambient temperature with the simple and easy-to-handle precatalyst Pd-II-acetate under ligand- and base-free conditions. Notable features are high isolated yields as well as regio- and stereoselectivities, and short reaction times. In a comparative investigation, aryl iodides, bromides and triflates were shown to be inferior coupling reagents in this reaction. The 3-arylmethylidene pyrrolidine-2,5-diones undergo a second Matsuda-Heck coupling, which proceeds via an endo-selective β-H-elimination to give diarylmethyl substituted maleimides as coupling products. These products can also be accessed in one flask by sequential addition of different arene diazonium salts to the starting itaconimide. The potential of 3-arylmethylidene succinimides as photoswitches was tested. Upon irradiation of the E-isomer at 300 nm partial isomerization to the Z-isomer (E : Z = 65 : 35 in the photostationary state) was observed. The isomerization was found to be nearly completely reversible by irradiating the mixture at 400 nm

Photochemical Synthesis and Properties of 1,6- and 1,8-Naphthalenophanes

Various 1,6- and 1,8-naphthalenophanes were synthesized by using the Photo-Dehydro-Diels-Alder (PDDA) reaction of bis-ynones. These compounds are easily accessible from w-(3-iodophenyl)carboxylic acids in three steps. The obtained naphthalenophanes are axially chiral and the activation barrier for the atropisomerization could be determined in some cases by means of dynamic NMR (DNMR) and/or dynamic HPLC (DHPLC) experiments

First example of an atropselective dehydro-Diels-Alder (ADDA) reaction

A new concept of a stereoselective synthesis of axially chiral biaryls, formed in the course of the dehydro-Diels-Alder (DDA) reaction, has been disclosed. It is based on asymmetric induction of the newly formed chirality axis by a chirality center, which is present in the two synthesized DDA reactants. Depending on the different length of the linkers joining the alkyne moieties the DDA reaction may be triggered photochemically or thermally, where only the thermal variant was stereoselective

Articulated rods – a novel class of molecular rods based on oligospiroketals (OSK)

We developed a new type of molecular rods consisting of two (or more) rigid units linked by a flexible joint. Consequently we called these constructs articulated rods (ARs). The syntheses of ARs were carried out by a flexible and modular approach providing access to a number of compounds with various functionalizations in terminal positions. First applications were presented with pyrene, cinnamoyl and anthracenyl labelled ARs

Building Blocks for Oligospiroketal (OSK) Rods and Evaluation of Their Influence on Rod Rigidity

We report on the synthesis of three new sleeves and their incorporation in OSK rods. The structures of these sleeves are based on <i>neo</i>-inositol, terephthalaldehyde diacetals, and indacene. To quantify the influence of the sleeves on rod rigidity, we applied the worm-like chain (WLC) model on the new rods and found that this approach is rather disappointing. As the chief cause of this result, we assume that the rigidity of typical molecular rods largely exceeds the rigidity of polymers, which were successfully described by the WLC model. Alternatively, we suggest quantifying the rigidity of molecular rods by fitting an empirical function on the end-to-end distance distribution curve obtained by MD simulations. After checking various function types, the Levy–Martin function proved to be most suitable for this purpose. On the basis of this function, we defined the Levy–Martin parameter and suggest using this parameter for the characterization of the rigidity of molecular rods