Szaloki, G.; (2012) Part I: Synthesis of novel purely planar chiral ferrocenes for aysymetric synthesis: Part II: Synthesis of novel azaferrocenylboronic acids. Doctoral thesis , UCL (University College London).

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Abstract

Part I : Synthesis of Novel Purely Planar Chiral Ferrocenes for Asymmetric Synthesis The first part of the thesis describes the design and synthesis of a series of 1,2-bidendate purely planar chiral ferrocenyl ligand (Ligand A, B, C). The planar chirality was established using Kagan’s Directed ortho Metallation (DoM) strategy. Introduction of the desired α–cyclopentadienyl moiety proved to be difficult using nucleophilic substitution. This was circumvented by utilising Stone’s fulvene formation method, followed by reduction of the corresponding fulvene. The synthesised ligands were then subjected to complexation studies. In general, the obtained complexes proved to be unstable. Despite the instability issue, their activity was tested in several asymmetric catalytic processes (Diels-Alder reaction, reconstitutive condensation, allylic substitution), however no enantio-induction was detected. In the course of extending the scope of the Stone method, it was applied to different cyclopentadienyl type (indenyl, fluorenyl, tetramethylcyclopentadienyl) systems successfully. In addition, the synthesis of a novel ferrocene linked dimer is given. This ligand showed moderate activity in allylic alkylation reaction. Part II : Synthesis of Novel Azaferrocenylboronic Acids Based on Whiting’s preliminary report a novel azaferrocenylboronic acid structure was envisaged. The best synthetic approach consisted of two steps. The aryl functionality was introduced at the 2-position of the azaferrocene ring in a Negishi cross coupling reaction, which was followed by a lithium-halogen exchange/boronylation sequence. Boronylations under different conditions were tested, however, isolation of the target boronic acid was unsuccessful probably due to its instability. Introduction of the borane functionality was achieved by using a modified boronylating agent and the resulting azaferrocenylborane proved to be stable. A monohydroxyboronic acid was isolated, which might be a candidate for asymmetric direct amide bond forming reactions.

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