We
have designed
and realized an efficient and operationally simple
single-flask synthesis of imidodiphosphate-based Brønsted acids.
The methodology proceeds
via
consecutive chloride
substitutions of hexachlorobisphosphazonium salts, providing rapid
access to imidodiphosphates (IDP), iminoimidodiphosphates (
i
IDP), and imidodiphosphorimidates (IDPi). These privileged
acid catalysts feature a broad acidity range (p
K
a
from ∼11 to <2 in MeCN) and a readily tunable confined
active site. Our approach enables access to previously elusive catalyst
scaffolds with particularly high structural confinement, one of which
catalyzes the first highly enantioselective
(>95:5 er) sulfoxidation of methyl
n
-propyl sulfide.
Furthermore, the methodology delivers a novel, rationally designed
super acidic catalyst motif, imidodiphosphorbis(iminosulfonylimino)imidate
(IDPii), the extreme reactivity of which exceeds commonly employed
super-Brønsted acids, such as trifluoromethanesulfonic acid.
The unique reactivity of one such IDPii catalyst has been demonstrated
in the first α-methylation of a silyl ketene acetal with methanol
as the electrophilic alkylating reagent.