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Spirocyclic diindenothiophenes were prepared by cyclization of tosylhydrazones, readily available from ketones, with 3,4-dibromo-2,5-bis(2-bromphenyl)thiophene. For bicyclic ketones, the bis-spirocycles were formed with very good diastereoselectivity. [ABSTRACT FROM AUTHOR]

The reaction of the singlet biradical [P(μ-NTer)]2 with various aldehydes selectively yielded the corresponding [2.1.1]-bicyclic addition products in a very fast reaction. All products were fully characterized, including by NMR and vibrational spectroscopy as well as single-crystal X-ray diffraction. The mechanism of the addition was investigated theoretically using high-level ab initio methods (CCSD(T) with triple- and quadruple-zeta basis sets) and corresponds to a concerted cycloaddition reaction with a very low activation barrier. For comparison, the mechanisms of the literature-known cycloadditions of H2, alkenes, and alkynes were also studied, indicating a similar reaction profile for all unsaturated reactants. [ABSTRACT FROM AUTHOR]

The reaction of the singlet biradical [P(μ-NTer)]2 with various aldehydes selectively yielded the corresponding [2.1.1]-bicyclic addition products in a very fast reaction. All products were fully characterized, including by NMR and vibrational spectroscopy as well as single-crystal X-ray diffraction. The mechanism of the addition was investigated theoretically using high-level ab initio methods (CCSD(T) with triple- and quadruple-zeta basis sets) and corresponds to a concerted cycloaddition reaction with a very low activation barrier. For comparison, the mechanisms of the literature-known cycloadditions of H2, alkenes, and alkynes were also studied, indicating a similar reaction profile for all unsaturated reactants. [ABSTRACT FROM AUTHOR]

The palladium(0)-catalyzed Suzuki cross-coupling reaction of the bis(triflates) of methyl 2,5-dihydroxybenzoate and methyl 2,4-dihydroxybenzoate afforded para- and meta-terphenyls, respectively. The reactions proceeded with very good site selectivity in favor of the sterically less hindered carbon atom. Key words: terphenyls, cross-coupling, palladium, site selectivity, Suzuki reaction. La reaction de couplage croise de Susuki des bis(triflates) de methyl 2,5-dihydroxybenzoate et de methyl 2, 4-dihydroxybenzoate catalysee au palladium(O) a donne les para-et meta-terphenyles, respectivement. Les reactions se sont deroulees avec une tres bonne selectivite de site en faveur de l'atome de carbone steriquement le moins encombre. [Traduit par la Redaction] Mots-cles: terphenyles, couplage croise, palladium, selectivite de site, reaction de Suzuki., Introduction Functionalized p-terphenyls occur in a great variety of pharmacologically relevant natural products. Examples include terphenyllin, (1) terprenin, (2) curtisian A, (3) leucomentin- (6,4) thelephorin A, (5) ganbajunin D, (6) [...]

The activation of C−Br bonds in various bromoalkanes by the biradical [⋅P(μ‐NTer)2P⋅] (1) (Ter=2,6‐bis‐(2,4,6‐trimethylphenyl)‐phenyl) is reported, yielding trans‐addition products of the type [Br−P(μ‐NTer)2P−R] (2), so‐called 1,3‐substituted cyclo‐1,3‐diphospha‐2,4‐diazanes. This addition reaction, which represents a new easy approach to asymmetrically substituted cyclo‐1,3‐diphospha‐2,4‐diazanes, was investigated mechanistically by different spectroscopic methods (NMR, EPR, IR, Raman); the results suggested a stepwise radical reaction mechanism, as evidenced by the in‐situ detection of the phosphorus‐centered monoradical [⋅P(μ‐NTer)2P‐R].< To provide further evidence for the radical mechanism, [⋅P(μ‐NTer)2P‐Et] (3Et⋅) was synthesized directly by reduction of the bromoethane addition product [Br‐P(μ‐NTer)2P‐Et] (2 a) with magnesium, resulting in the formation of the persistent phosphorus‐centered monoradical [⋅P(μ‐NTer)2P‐Et], which could be isolated and fully characterized, including single‐crystal X‐ray diffraction. Comparison of the EPR spectrum of the radical intermediate in the addition reaction with that of the synthesized new [⋅P(μ‐NTer)2P‐Et] radical clearly proves the existence of radicals over the course of the reaction of biradical [⋅P(μ‐NTer)2P⋅] (1) with bromoethane. Extensive DFT and coupled cluster calculations corroborate the experimental data for a radical mechanism in the reaction of biradical [⋅P(μ‐NTer)2P⋅] with EtBr. In the field of hetero‐cyclobutane‐1,3‐diyls, the demonstration of a stepwise radical reaction represents a new aspect and closes the gap between P‐centered biradicals and P‐centered monoradicals in terms of radical reactivity. [ABSTRACT FROM AUTHOR]

The oxidation of silylated hydrazine, (Me3Si)2N−N(H)SiMe3, with silver salts led to the formation of a highly labile hydrazinium‐yl radical cation, [(Me3Si)2N−N(H)SiMe3].+, at very low temperatures (decomposition > −40 °C). EPR, NMR, DFT and Raman studies revealed the formation of a nitrogen‐centered radical cation along the N−N unit of the hydrazine. In the presence of the weakly coordinating anion [Al{OCH(CF3)2}4]−, crystallization and structural characterization in the solid state were achieved. The hydrazinium‐yl radical cation has a significantly shortened N−N bond and a nearly planar N2Si3 framework, in contrast to the starting material. According to DFT calculations, the shortened N−N bond has a total bond order of 1.5 with a π‐bond order of 0.5. The π bond can be regarded as a three‐π‐electron, two‐center bond. [ABSTRACT FROM AUTHOR]

The oxidation of silylated hydrazine, (Me3Si)2N−N(H)SiMe3, with silver salts led to the formation of a highly labile hydrazinium‐yl radical cation, [(Me3Si)2N−N(H)SiMe3].+, at very low temperatures (decomposition > −40 °C). EPR, NMR, DFT and Raman studies revealed the formation of a nitrogen‐centered radical cation along the N−N unit of the hydrazine. In the presence of the weakly coordinating anion [Al{OCH(CF3)2}4]−, crystallization and structural characterization in the solid state were achieved. The hydrazinium‐yl radical cation has a significantly shortened N−N bond and a nearly planar N2Si3 framework, in contrast to the starting material. According to DFT calculations, the shortened N−N bond has a total bond order of 1.5 with a π‐bond order of 0.5. The π bond can be regarded as a three‐π‐electron, two‐center bond. [ABSTRACT FROM AUTHOR]