Preparation of an Indolylfulgimide‐Adamantane Linker Conjugate with Nitrile Anchoring Groups through Palladium‐Catalyzed Transformations

We report the preparation, through palladium-catalyzed transformations, of the indolylfulgimide linker conjugate 1, containing an adamantane core and nitrile anchoring groups. The ethynylene-linker 12 for the final Sonogashira coupling was prepared through palladium-mediated cyanation of an iodo-substituted precursor with Zn(CN)2. The synthesis of the 6-bromo-substituted indolylfulgimide coupling partner 2 was accomplished in seven steps. Model studies using phenylacetylene and the 5-bromo-substituted indole 13 were conducted to find conditions that would prevent homocoupling of the ethynylene linker 12 in the final Sonogashira coupling step. The use of Pd(PhCN)2Cl2 and [(tBu)3PH]BF4 in the presence of diisopropylamine, together with CuI as additive, proved to be most efficient. Finally, the photochromic properties of conjugate 1 and indolylfulgimide 2 were studied.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)