Visible‐light irradiation (λ=457 nm) enabled the enantioselective ortho photocycloaddition of olefins to phenanthrene‐9‐carboxaldehydes (15 examples, 46–93 % yield, 82–98 % ee). A chiral oxazaborolidine Lewis acid (20 mol %) was employed as the catalyst. It operates by coordination to the aldehyde inducing a bathochromic absorption shift beyond the nπ* absorption of the uncomplexed aldehyde. At long wavelengths the Lewis acid complex is exclusively excited; within the complex, one enantiotopic face of the aromatic aldehyde is efficiently shielded. Lewis acid coordination also alters the type selectivity and the simple diastereoselectivity of the photocycloaddition.

Cascade (domino) reactions facilitate the formation of complex molecules from simple starting materials in a single operation. It was found that 1-naphthaldehyde derivatives can be converted to enantioenriched (82-96% ee)...

Die Bestrahlung mit sichtbarem Licht (l = 457 nm) ermçglicht eine enantioselektive ortho-Photocycloaddition von Olefinen an Phenanthren-9-carbaldehyde (15 Beispiele, 46-93 %Ausbeute,82-98 %ee). Eine chirale Oxazaborolidin-Lewis-Säure (20 mol %) wurdeals Katalysator verwendet, die durch Koordination an den Aldehyd eine bathochrome Verschiebung der Absorption bewirkt, die über die ursprüngliche np*-Absorption des unkomplexierten Aldehyds hinausgeht. Bei großer Wellenlänge wird ausschließlichd er Lewis-Säure-Komplex angeregt und eine der beiden enantiotopen Seiten des aromatischen Aldehyds wird effizient abgeschirmt. Die Lewis-Säure-Koordination verändert überdies die Typselektivitätund die einfacheD iastereoselektivitätder Photocycloaddition.

Lewis acids, such as AlBr3, completely alter the photochemical behaviour of naphthaldehydes. Instead of typical carbonyl photochemistry, the aldehydes undergo cycloaddition reactions at the arene core upon visible-light irradiation.

In the coordination chemistry of palladium, dimers bridged via halides are a common motif. Higher oligomers, however, are still rare. We report the structure of an alternating eight-membered [Pd4Br4](4-) ring framed by cycloheptatrienide ligands, which was obtained by cocrystallization of dimers and tetramers of the complex salt bromido{η(3)-[3-(2,6-diisopropylphenyl)imidazolium-1-yl]cycloheptatrienido}palladium(II) tetrafluoroborate, namely bis[di-μ-bromido-bis({η(3)-[3-(2,6-diisopropylphenyl)imidazolium-1-yl]cycloheptatrienido}palladium(II))] cyclo-tetra-μ-bromido-tetrakis({η(3)-[3-(2,6-diisopropylphenyl)imidazolium-1-yl]cycloheptatrienido}palladium(II)) octakis(tetrafluoroborate) dichloromethane octasolvate, [Pd4Br4(C22H26N2)4][Pd2Br2(C22H26N2)2]2(BF4)8·8CH2Cl2. These dimers and tetramers form a highly dynamic equilibrium in solution which was studied by low-temperature NMR spectroscopy. In the light of the presented results, tetrameric Pd(II) species can be assumed to co-exist as a second species in many cases where by current knowledge only a dimeric compound would be expected.