New Ways of Diamondoid Functionalization – A Synthetic Method for the Incorporation of Dispersion Energy Donors into Catalysts and Molecular Balances

Abstract

This thesis deals with the selective functionalization of diamondoids and their incorporation in existing catalytic systems as well as molecular balances to quantify London dispersion interactions. In the first part, we present a new substitution reaction based on the Mitsunobu reaction. This sequence works particularly well for lower diamondoids, like adamantane and diamantane, with high yields and good reaction control. Abundant alcohols react to diphenylphosphinite structures. The corresponding diamondoid based trivalent phosphorous compounds are insensitive towards air and moisture and therefore ideal storable precursors. The reaction of the phosphinites with diisopropylazodicarboxylate as activating agent leads to an intermediate betaine structure. The latter collapses upon protonation by a mildly acidic nucleophile, to a carbocation. This cation is trapped by the deprotonated nucleophile leading to the desired target compound. The reaction sequence is universal for all structures that can form a stabilized carbocation intermediate and works well for a broad variety of pronucleophiles. Therefore it offers the possibility of nearly every C−C or C−heteroatom bond formation reaction. Mechanistic studies underline the formation of a carbocation intermediate, which has not been reported in all redox condensation reactions published so far. The second part of this thesis deals with a new uniform synthesis concept towards all-meta substituted iodobenzenes and anilines. 3,5-Disubstituted catechols serve as starting materials and were synthesized via formylation of the corresponding 2,4-disubstituted phenols and subsequent Dakin reaction. After oxidation of the dihydroxybenzenes, the o quinones react in a [4+2] cycloaddition with an alkyne to a bicyclic 1,2-diketone. Final photodecarbonylation with visible light yield the 1,3,5-trisubstituted scaffold which is further manipulated to the desired targets via known reactions, e.g., Schmidt reaction. The new type of substitution reaction from the first part of this thesis was crucial for the generation of the 3,5-disubstituted diamondoid precursors since the corresponding phenol structure was not available and the sequence described before was not applicable to adamantane and diamantane substituted compounds. This underlines the importance of suitable reaction sequences that also enable the incorporation of diamondoids into existing structures. We applied our new scalable reaction pathway in the synthesis of chiral BINOL-based phosphoric acid catalysts, substituted with all-meta adamantyl and diamantyl arenes. In a comparative study, this new bulky catalyst performed equally well in comparison to existing catalysts in the reductive amination reaction of acetophenone and delivers enantiomeric excesses of up to 84% without optimization of the reaction conditions.