Synthesis of Chiroptical Molecular Switches by Pd-Catalyzed Domino Reactions Lutz F. Tietze,* ,† Alexander Du ¨ fert, † Florian Lotz, † Lars So ¨ lter, ‡ Kawon Oum, ‡ Thomas Lenzer, ‡ Tobias Beck, § and Regine Herbst-Irmer § Institut fu ¨r Organische und Biomolekulare Chemie, Georg-August-UniVersita ¨t Go ¨ttingen, Tammannstrasse 2, D-37077 Go ¨ttingen, Germany, Institut fu ¨r Physikalische Chemie, Georg-August- UniVersita ¨t Go ¨ttingen, Tammannstrasse 6, D-37077 Go ¨ttingen, Germany, and Institut fu ¨r Anorganische Chemie, Georg-August-UniVersita ¨t Go ¨ttingen, Tammannstrasse 4, D-37077 Go ¨ttingen, Germany Received August 6, 2009; E-mail: ltietze@gwdg.de Abstract: 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. Introduction The development of organic compounds that allow a con- trolled motion at the molecular level is an important prerequisite for the construction of nanoswitches and nanomotors. 1,2 Based on today’s requirements in the miniaturization of data storage devices and the concomitant success of digital optical data systems, in which recording and read-out of information is carried out by light, the shift from classic electronic semicon- ductor elements to light-driven molecular switches has gained great impetus. This is underlined by the development of new information storage techniques, fabrication processes and novel synthetic methodologies in the past years. 3 The advantage in using inorganic compounds for data-storage devices is the long-term knowledge and experience of their fabrication, but they lack some desirable properties such as. e.g. the fine-tuning of a large variety of physical properties or the characterization of single isolated structures. On the other hand, organic compounds can overcome such deficiencies with the embedded advantage of solving problems such as decreased thermal and photochemical stability by small structural modifications. The basic requirement for a molecular switch is bistability, in which both forms can be interconverted by means of external stimuli such as light, heat, pressure, magnetic or electric fields, pH change or chemical reactions. 2a,4 Moreover, one must be able to selectively address both forms individually and detect them separately, preferably on very short time scales to allow their potential use in modern computing machines. 5 The chiroptical switches developed by Feringa et al. (e.g., 1) containing a helical tetra-substituted alkene moiety are particu- larly promising since their stable states can be accessed using circularly polarized light (Scheme 1). 6 Quite recently, tetra-substituted alkenes have also been prepared by Lautens, Florent and Yu. 7 Here we describe an efficient and general access to novel compounds of type 2 with a helical backbone using Pd-catalyzed † Institut fu ¨r Organische und Biomolekulare Chemie. ‡ Institut fu ¨r Physikalische Chemie. § Institut fu ¨r Anorganische Chemie. (1) (a) Balzani, V.; Venturi, M.; Credi, A. Molecular DeVices and Machines: A Journey into the Nanoworld, Wiley-VCH: Weinheim, 2003. (b) Acc. Chem. Res. 2001, 34, 409-522 (Molecular Machines special issue). (2) (a) Feringa, B. L., Ed.; Molecular Switches; Wiley-VCH: Weinheim, 2001. (b) Crano, J. C.; Guglielmetti, R. J.; Organic Photochromic and Thermochromic Compounds; Springer: New York, 1999, Vols. 1-3. (c) Feringa, B. L.; van Delden, R. 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