New photochromic switches based on helical alkenes can quickly and efficiently be accessed by Pd-catalyzed domino reactions using a modular approach; this allows a wide variability in product formation with the advantages of a convergent synthetic route. The alkenes have been synthesized in excellent enantioselectivity and their switching properties assessed by stimulation with nanosecond laser pulses at two different wavelengths in over 1000 switching cycles.

The palladium-catalysed domino cyclisation of the aryl bromides 4, containing an alkyne and a bromonaphthyl moiety, leads to tetracycles of type 5 in good yields. The substrates 4 are easily accessible by addition of the corresponding lithiated alkynes 7 to the aldehyde 6.

Pd-Catalyzed Domino Arylation/CH Activation for the Synthesis of Acenaphthylenes. -The cyclization of the aromatic alkynes (IIIa)-(IIIc) gives the acenaphthylenes (IVa)-(IVc) in good yields without the need for protection of the hydroxy group. Aliphatic alkynes such as (IIId) can also be used, albeit with lower yield. Sterically hindered alkynes such as (IIIe) or the tert-butyl derivative (V) do not react or undergo only the first C-C bond formation step. -(TIETZE*, L. F.; LOTZ, F.; Eur.

Proximity effects permit C–H activation reactions without directing groups. Here competitive reactions of selected substrates were investigated which allow a domino‐carbopalladation/Mizoroki–Heck reaction and a domino‐carbopalladation/C–H activation reaction. In the Pd‐catalyzed transformation of the enantio‐ and diastereopure alkyne 8a the tetra‐substituted alkenes 10 and 11 were formed almost exclusively through a domino carbopalladation/Mizoroki–Heck reaction. In contrast, the diastereomer 8c only led to the acenaphthylenes 12c and 13c through a domino carbopalladation/C–H activation reaction. Moreover, in the reaction of 20, 24 and 27 containing a naphthyl moiety only the tetra‐substituted alkenes 23, 25/26 and 28/29, respectively were obtained, whereas in the reaction of 34, containing a phenanthrene moiety, compound 37 was the only product, formed via a C–H activation reaction.

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