Reactions triggered by light constitute a treasure trove of unique synthetic methods that are available to chemists. Photoinduced redox processes using visible light in conjunction with sensitizing dyes offer a great variety of catalytic transformations useful in the realm of organic synthesis. The recent literature amply shows that this preparative toolbox is expanding substantially. This review discusses historical and contemporary work in the area of photoredox catalysis with [Ru(bpy)3]2+. Elegant examples from the most recent literature document the importance of this fast developing area of research. The photoredox chemistry has also emerged as a promising bond-making and bond-breaking tool for chemical biology and materials chemistry. A review with 96 references.

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A nonphotochemical synthetic route to 3-hexahelicenol is reported. It involves a key [2+2+2] cycloisomerization of CH3O-substituted triyne that is readily available from 1-methoxy-3-methylbenzene and 1-bromo-2-(bromomethyl)naphthalene. Further functional group transformations led to 3-CO2CH3, 3-NH2, 3-PPh2, and 3-SC(O)N(CH3)2 substituted hexahelicenes.

Helicenes have attracted attention as unique inherently chiral three-dimensional aromatic compounds for several decades. Despite significant recent progress in the synthesis and applications of carbohelicenes and thiaheterohelicenes, [1] the potential of the aza analogues with a pyridine unit (pyridohelicenes) have not been explored. [2,3] There are only scattered examples of the preparation of pyridohelicenes, [4] but with no general synthetic methodology, since the photochemical approach can fail with pyridohelicenes [4b,c,e] while non-photochemical alternatives can be difficult to adapt to the synthesis of N-heteroaromatic compounds. The properties and chemical behavior of pyridohelicenes are practically unknown apart from their basicities [4e,g] and the self-assembly [5] of certain derivatives. Nevertheless, promising applications of pyridohelicenes in various branches of chemistry and material science might be envisaged and, therefore, further research in the field is required.Recently, we observed remarkably high proton affinities of pyridohelicene derivatives, as measured by mass spectrometric techniques.[6] In the gas phase, helically chiral 1-aza[6]helicene (2, Scheme 1), for example, exhibits a comparable proton affinity (1000 kJ mol À1 ) to 4-(dimethylamino)-pyridine (DMAP, 997 kJ mol À1 ). Herein, we report the practical syntheses of 1,14-diaza[5]helicene (1), [7] 1-aza[6]helicene (2), [8] and 2-aza[6]helicene (3).[9] Moreover, we have succeeded in resolving racemates of 2 and 3 into their enantiomers, assigning their absolute configuration, determining the energy barriers to racemization, and obtaining Xray structures of their corresponding silver complexes. The strategy for the preparation of 1-3 relies on a [2+2+2] cyclotrimerization of an aromatic triyne in the presence of a Co I catalyst to build the helical scaffold. We have already proven that such a methodology is robust and reliable for the preparation of helicenes and their analogues.[10] Thus, the straightforward synthesis of 1 started from the readily accessible bromopyridine 4, [11] which was treated with lithiated 1-(triisopropylsilyl)-1-propyne to yield 5 which contained an attached alkyne side arm (Scheme 2). Sonoga-