Benzene (E 0 = À3.42 V vs. a saturated calomel electrode, SCE [1] ) and its close analogs are among the most challenging organic substrates for reduction. Very few chemical entities have the power to add an electron to ground-state benzene, and these are all derived from highly reactive metals. Thus, the alkali metals sodium (E 0 = À2.71 V) and lithium (E 0 = À3.04 V) dissolve in liquid ammonia to form solvated electrons together with the corresponding metal cations, [2] and similarly calcium (E 0 = À2.89 V) and lithium dissolve in aliphatic amines.[3] These solvated electrons can convert benzene to its radical anion. In the Birch reduction, a protonation step follows for the arene radical anion, but this step is independent of the electron-rich metal. Very recently, a complex derived from samarium(II) iodide, also in the presence of an amine, joined this exclusive set of reagents, in the reduction of the substrate, 4-methoxybenzyl alcohol. [4,5] We now explore whether a completely organic molecule can convert close analogs of benzene to their radical anions, mirroring the behavior of the metals described above. The choice of arene substrate determines the level of the challenge. E 0 values are not routinely available for benzenes, [1] other than those activated by electron-withdrawing groups. However, comparison of the computed lowest unoccupied molecular orbital (LUMO) energies of a range of arenes shows [6] (see Table S1 in the Supporting Information) that benzenes substituted by saturated carbon groups have LUMO energies that lie within 0.2 eV of the value for benzene itself. In contrast, both extended arenes and arenes substituted by electron-withdrawing groups (e.g. CN, CO 2 Me) have much lower LUMO energies and are much easier to reduce. Accordingly, in choosing a discriminating test for a reducing agent, the latter substrates are not appropriate. We have chosen 1,2-diphenylcyclopropanes 4 and 5 and their derivatives 6-11 as the substrates for our study. Both 4 and 5 have LUMO energies within 0.2 eV of that of benzene, are relatively involatile, and can report the intermediacy of radical anions through the opening of the cyclopropane ring (see Scheme 1).Our recent research has probed the ground-state donor properties of highly reactive neutral organic reducing agents. Thus, we have shown that the neutral ground-state organic electron donor 1 [7,8] (Scheme 1) reduces iodoarenes [9,10] to aryl radicals [11] while the stronger donors 2[12] and 3 [13] under milder conditions, afford aryl anions from the same substrates Scheme 1. Reactions of organic electron donors with substrates.

Allylic amides and their derivatives represent a versatile class of nitrogen-containing building blocks, the bifunctional nature of which has enabled a diverse array of transformations and established them as strategically important molecules in chemical synthesis. [1,2] Particularly useful are reactions where an electrophile activates the carbon-carbon double bond towards attack of the pendant oxygen atom of the amide carbonyl group to form either a five or sixmembered ring heterocycle, depending on the mode of cyclization (Scheme 1 a). [3] Most of these reactions are triggered by heteroatom electrophiles, often activated by a catalyst, and result in the formation of a carbon-oxygen and a carbon-heteroatom bond. It is, however, surprising that the related electrophilic carbofunctionalization process is rare. One possible reason for this is the lack of suitable carbon electrophiles that can activate the carbon-carbon double bond of the allylic amide. The development of Pd-catalyzed oxyarylation and aminoarylation reactions, in particular by Wolfe and co-workers, [4] as well as related Pd, [5] Cu, [6] and Aucatalyzed [7] processes have provided an alternative approach to related alkene difunctionalization [8] and can be applied to derivatives of the generic allylic amine framework. Despite these advances, the development of novel methods that catalytically generate carbon electrophiles capable of activating alkenes to nucleophilic attack remains a challenge; the solution to this challenge would be of significant use in complex molecule synthesis.As part of an overarching program aimed at the exploitation of high oxidation state metal species we, [9] and others, [10] have established that the combination of copper catalysts and diaryliodonium salts gives rise to a high oxidation state Cu III / aryl [11] intermediate that displays reactivity of an aromatic electrophile (Scheme 1 b). We reasoned that this distinct catalytic activation strategy could be used to generate the aromatic electrophile equivalent that would be needed to affect an intramolecular oxyarylation of allylic amides, thus complementing the corresponding heteroatom electrophile triggered cyclizations that have become a mainstay in synthesis.We selected aryl-substituted allylic amides with which to test our copper-catalyzed oxyarylation strategy as the products would generate a broadly useful class of diarylated amino alcohols. Furthermore, we noted that some aryl-substituted allylic amides have been utilized in other electrophile triggered cyclization reactions. For example, treatment with acid induces an intramolecular hydration-type reaction to form the 6-membered-ring oxazine product (Scheme 1 c). [13] Similarly, treatment with bromine gives rise to a bromocyclization, again forming the oxazine product, although this is dependent on the geometry of the starting alkene and the electronic nature of the aromatic ring. [14,15] To the best of our knowledge, there are no examples of such a catalytic electrophilic carbofunctionalization of this class of ...

The first crown-tetracarbene complex of Ni(II) has been prepared, and its crystal structure determined. The complex can be reduced by Na/Hg, with an uptake of two electrons. The reduced complex reductively cleaves arenesulfonamides, including those derived from secondary aliphatic amines, and effects Birch reduction of anthracenes as well as reductive cleavage of stilbene oxides. Computational studies show that the orbital that receives electrons upon reduction of the complex 2 is predominantly based on the crown carbene ligand and also that the HOMO of the parent complex 2 is based on the ligand.

A catalytic enantioselective and regiodivergent arylation of alkenes is described. Chiral copper(II)bisoxazoline complexes catalyze the addition of diaryliodonium salts to allylic amides in excellent ee. Moreover, the arylation can be controlled by the electronic nature of the diaryliodonium salt enabling the preparation of nonracemic diaryloxazines or β,β′-diaryl enamides.

Leistungsstarke Reduktionen: Einfache organische Elektronendonoren, die einzig aus den Elementen Kohlenstoff, Wasserstoff und Stickstoff bestehen, reduzieren nach Anregung mit Licht Benzolringe, die sich im Grundzustand befinden, zu Radikalanionen (DMF=Dimethylformamid).