Abstract
This work focuses on the conceptual development of highly confined, super acidic Brønsted
acids and their application in asymmetric catalysis. A new synthetic strategy to access
imidodiphosphate-derived Brønsted acids based on a toolbox principle has been developed.
This methodology proceeds via consecutive chloride substitutions of
hexachlorobisphosphazonium salts, providing rapid access to privileged catalyst motifs, such
as imidodiphosphates (IDP), iminoimidodiphosphates (iIDP), and imidodiphosphorimidates
(IDPi). Furthermore, this approach enables access to previously elusive catalyst scaffolds with
particularly high structural confinement, allowing the highly enantioselective transformation of
small and structurally unbiased substrates, as exemplarily demonstrated in the asymmetric
sulfoxidation of propyl methyl sulfide. To access extremely acidic catalyst motifs, a new
synthesis of arylbis(trifluoromethylsulfonylimino)sulfonamides has been developed, which
upon implementation into the imidodiphosphate-framework led to the development of
imidodiphosphorbis(iminosulfonylimino)imidates (IDPii). Combinatorial spectroscopic and
experimental data reveal higher acidities of the novel IDPii motif than commonly employed
super acids, such as trifluoromethanesulfonic acid or bis(trifluoromethanesulfonyl)imide. Most
notably, IDPiis allow rendering alcohols into strong electrophilic alkylating reagents under
silylium activation, as it has been exemplarily demonstrated in the α-methylation of silyl ketene
acetals – transforming methanol into a strong electrophilic methyl surrogate. Although the
IDPii catalyst class displays extreme reactivity and overcomes previous limitations regarding
substrate activation, no sufficient enantioinduction was observed in the explored asymmetric
transformations. Crystallographic analyses of several IDPii catalysts motifs illustrated
insufficient BINOL-induced structural confinement. Considered as a solution, a monovalent
chiral catalyst scaffold has been conceptually designed, which in combination with the new
access of bis(trifluoromethylsulfonylimino)sulfonyl units was believed to give access to a novel
extremely Brønsted acidic and highly selective catalyst class. This catalyst design focuses on
the tetrahydroindacene motif with two adjacent appendages to confine the active site. Herein, a
seminal contribution toward the conceptual design, the synthesis and potential application of
this unprecedented catalyst scaffold is disclosed.
