A new efficient synthesis of indolo3,2,1-jkcarbazoles by the palladium-catalyzed cyclization of N-(2-bromoaryl)carbazoles is described. The reaction involves intramolecular C–C bond formation, ...coupled with the cleavage of a C–X bond and a C–H bond on carbazole ring. Substitutions on N-aryl core with either electron-donating or electron-withdrawing groups are introduced, and different reaction factors for cyclization are evaluated.
The synthesis and crystal structures of 1-(5-methyl-1H-indol-6-yl)ethan-1-one (7), C11H11NO, and 1-3-(dimethylamino) methyl-5-methyl-1H-indol-6-ylethan-1-one (8), C14H18N2O, are reported. The ...synthesis is based on the Diels-Alder cycloaddition of a substituted 2H-pyran-2-one derivative, followed by an acid-catalyzed cyclization and concomitant deprotection (the last two steps were carried out as a one-pot domino process) yielding substituted indole 7, which was further derivatized via Mannich reaction to the gramine derivative 8. Both structures 7 and 8 were determined on the basis of IR, 1H NMR and mass spectroscopy, as well as by the elemental analysis and melting point determination. According to the single-crystal X-Ray diffraction analysis, the structure 7 has a single unique molecule in the asymmetric unit whereas the structure 8 contains four unique molecules in the asymmetric unit. Molecules 7 are linked via N-H···O hydrogen bonds between the secondary amine group and carbonyl moiety of the acetyl group of adjacent molecules, whereas molecules 8 are linked via N-H···N hydrogen bonds between the secondary and tertiary amine groups of adjacent molecules. Both structures are further stabilized by weak C-H···O, C-H···π and π···π interactions.
In Diels–Alder reactions, 2H-pyran-2-ones as dienes can yield a large variety of cycloadducts with up to four contiguous carbon stereogenic centers. Some of the potentially most useful, however ...difficult to prepare due to their low thermal stability, are the primary CO2-containing oxabicyclo2.2.2octenes, which could be formed as eight distinctive isomers (two sets of regioisomers, each of these composed of four different stereoisomers). A high-pressure synthesis of such products was recently described in a few cases where vinyl-moiety-containing dienophiles were used as synthetic equivalents of acetylene. However, structures of the primary products have been so far only rarely investigated in detail. Herein, we present seven novel single-crystal X-ray diffraction structures of such cycloadducts of both stereoisomeric forms, i.e., endo and exo. Additionally, we present a single-crystal structure of a rare case of a cyclohexadiene system stable at room temperature, obtained as a secondary product upon the retro-hetero-Diels–Alder elimination of CO2 under thermal conditions (microwave irradiation), during this elimination the symmetry is increased and out of eight initially possible isomers of the reactant, this number in the product is decreased to four. In oxabicyclo2.2.2octene compounds, centrosymmetric hydrogen bonding was found to be the predominant motif and diverse supramolecular patterns were observed due to rich variety of C–H⋯O and C–H⋯π interactions.
With the application of a double dienophile 1,1'-(hexane-1,6-diyl)bis(1H-pyrrole-2,5-dione) for a 4+2 cycloaddition with a substituted 2H-pyran-2-one a novel 26-membered tetraaza heteromacrocyclic ...system 3 was prepared via a direct method under solvent-free conditions with microwave irradiation. The macrocycle prepared is composed of two units of the dienophile and two of the diene. The structure of the macrocycle was characterized on the basis of IR, 1H and 13C NMR and mass spectroscopy, as well as by the elemental analysis and melting point determination. With X-ray diffraction of a single crystal of the macrocycle we have determined that the two acetyl groups (attached to the bridging double bond of the bicyclo2.2.2octene fragments) are oriented towards each other (and also towards the inside of the cavity of the macrocycle), therefore, mostly filling it completely.
A study of an unusual effect of the size of the ring fused to 2H-pyran-2-ones on the exo/endo selectivity of a thermal double cycloaddition of N-substituted maleimides or maleic anhydride yielding ...bicyclo2.2.2octene derivatives is presented. With subtle variations of starting compounds and reaction conditions exclusively exo,exo or exo,endo products can be prepared.
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