Triazenes are valuable compounds in organic chemistry and numerous applications have been reported. Furthermore, triazenes have been investigated extensively as potential antitumor drugs. Here, we describe a new method for the synthesis of triazenes. The procedure involves a reagent which is rarely used in synthetic organic chemistry: nitrous oxide (N2 O, "laughing gas"). Nitrous oxide mediates the coupling of lithium amides and organomagnesium compounds while serving as a nitrogen donor. Despite the very inert character of nitrous oxide, the reactions can be performed in solution under mild conditions. A key advantage of the new procedure is the ability to access triazenes with alkynyl and alkenyl substituents. These compounds are difficult to prepare by conventional methods because the required starting materials are unstable. Some of the new alkynyltriazenes were found to display high cytotoxicity in in vitro tests on ovarian and breast cancer cell lines.

No abstract

Vinyl triazenes were obtained by enantioselective [2+2] cycloaddition reactions of bicyclic alkenes with 1-alkynyl triazenes in the presence of a Ru catalyst with a chiral cyclopentadienyl ligand. These triazenes serve as unique vinyl cation surrogates. Under acidic conditions, the triazene functionality can be replaced with a variety of groups, including halides, alkoxides, sulfoxides, amides, arenes, and heteroarenes, thus providing efficient access to a pool of chiral polycyclic compounds.

Nitrous oxide ("laughing gas", N 2 O) is a potent oxidation agent, from a thermodynamic point of view. [1] Moreover, it is an environmentally benign oxidant, because the side product is dinitrogen. An obstacle in using N 2 O in oxidation reactions is the inert nature of the gas. Heterogeneous catalysts have been used with good success for the activation of N 2 O, but high temperatures and/or pressures are typically required to achieve acceptable reaction rates. [2] Thus far, N 2 O-based oxidation reactions with homogeneous catalysts in solution have met with only limited success. Many transition-metal complexes are known to react with N 2 O under mild conditions, [3] but catalytic turnover is difficult to achieve. Some polyoxometalates [4] and ruthenium complexes [5] were shown to catalyze oxidation reactions with N 2 O, but the reactions require high temperatures (100-200 8C) and often elevated pressures. [6] Furthermore, the reported turnover numbers are modest ( 100). Herein, we describe oxidative carbon-carbon coupling reactions with N 2 O, which can be performed under mild conditions with good selectivity and unprecedented turnover numbers.Oxidative homo-and cross-coupling reactions of Grignard reagents [7,8] in the presence of metal catalysts can be achieved with different oxidants, including 1,2-dihaloethanes [9] and dioxygen. [10] The reactions are believed to involve low-valent organometallic complexes. [7][8][9][10] We hypothesized that these low-valent, nucleophilic complexes might be susceptible to oxidation by N 2 O. As a model reaction, we studied the homocoupling of phenylmagnesium chloride. The reactions were performed in THF at room temperature under an atmosphere of N 2 O using different transition-metal salts as potential catalysts (Li 2 CuCl 4 , Li 2 MnCl 4 , CoCl 2 , FeCl 3 , [Fe(acac) 3 ]). To avoid reactions caused by traces of dioxygen, we have used N 2 O of high purity (99.999 %). Test reactions with metal salt (1 mol %) gave the oxidative coupling product biphenyl after 1 h in yields of 30-95 % (Table 1, entries 1-5). The best results were found for FeCl 3 (94 % yield), [Fe(acac) 3 ] (94 % yield) and CoCl 2 (95 % yield). The latter two complexes were used for further studies.First, we examined the efficiency of the reaction. Lowering the amount of catalyst from 1.0 mol % to 0.1 mol % had no effect on the yield. Further reduction to 0.01 mol % gave a poor yield in the case of [Fe(acac) 3 ], even if the reaction time was prolonged. With CoCl 2 , however, the catalyst loading could be reduced to 0.004 mol % and biphenyl was still obtained in 83 % yield (Table 1, entry 7). Taking into account the small amount of product formed without catalyst (8 % after 18 h), and assuming that one catalytic cycle produces one biphenyl molecule, we can calculate a turnover number of 9.4 10 3 . This value greatly exceeds what has been reported thus far for metal-catalyzed oxidation reactions with N 2 O in homogeneous solution. [4,5] The groups of Lei [10c] and Cahiez [10d] have shown that Fe complexes ar...

Kinetic and spectroscopic analyses were performed to gain information about the mechanism of atom-transfer radical reactions catalyzed by the complexes [RuCl2Cp*(PPh3)] and [RuClCp*(PPh3)2] (Cp*=pentamethylcyclopentadienyl), in the presence and in the absence of the reducing agent magnesium. The reactions of styrene with ethyl trichloroacetate, ethyl dichloroacetate, or dichloroacetonitrile were used as test reactions. The results show that for substrates with high intrinsic reactivity, such as ethyl trichloroacetate, the oxidation state of the catalyst in the resting state is +3, and that the reaction is zero-order with respect to the halogenated compound. Furthermore, the kinetic data suggest that the metal catalyst is not directly involved in the rate-limiting step of the reaction.