2,3-Dichloropyridine N-oxide, a novel
oxygen transfer
reagent, allows the conductance of the gold(I)-catalyzed oxidation
of alkynes to 1,2-dicarbonyls in the absence of any acid additives
and under mild conditions to furnish the target species, including
those derivatized by highly acid-sensitive groups. The developed strategy
is effective for a wide range of alkyne substrates such as terminal-
and internal alkynes, ynamides, alkynyl ethers/thioethers, and even
unsubstituted acetylene (40 examples; yields up to 99%). The oxidation
was successfully integrated into the trapping of reactive dicarbonyls
by one-pot heterocyclization and into the synthesis of six-membered
azaheterocycles. This synthetic acid-free route was also successfully
applied for the total synthesis of a natural 1,2-diketone.
The gold‐catalyzed interplay between cyanamides and ynamides demonstrates condition‐dependent mechanistic dichotomy. [2+2+2] Cycloaddition proceeds under kinetically controlled conditions to give 2,4,6‐triaminopyrimidines (19 examples, up to 99%). Under thermodynamically controlled conditions, the reactivity switches from [2+2+2]‐ to [4+2] cycloaddition; the latter [4+2] reaction accomplishes 1,3‐diaminoisoquinolines (19 examples, up to 97%). The advantages of both methods include regioselectivity, mild reaction conditions (even for the thermodynamically controlled [4+2] reaction) and the possibility of introducing a variety of dialkyl, diaryl, and heterocyclic amino substituents into the target pyrimidine and isoquinoline cores. The reactions were conducted on gram scales and the versatility of the obtained products was demonstrated by post‐functionalizations.magnified image
The gold-catalyzed reaction between
benzofuroxans, functioning as nitrene transfer reagents, and N-allylynamides leads to 3-azabicyclo[3.1.0]hexan-2-imines.
This highly selective annulation proceeds smoothly under mild conditions
(5 mol % Ph3PAuNTf2, PhCl, 60 °C) and exhibits
high functional group tolerance (21 examples, ≤96% yields).
The obtained cyclopropanated products represent a useful synthetic
platform with an easily modulated substitution pattern as illustrated
by their postmodifications. Intramolecular cyclopropanation of gold
α-imino carbene intermediates is suggested as a key step of
the catalytic cycle.
The developed modular approach to hard-to-reach non-aromatic 3H- and 2H-pyrroles is based on the integration of 2H-azirines and ynamides. Gold-catalyzed [3+2] cycloaddition of 2,2-disubstituted 2H-azirines and ynamides comprises a high...
Triflic acid (10 mol%) catalyzes the highly regioselective [2 + 2 + 2] cycloaddition between two cyanamides and one ynamide to grant the 2,4,6-triaminopyrimidine core.
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