Gold-Catalyzed Stereoselective Synthesis of Azacyclic Compounds through a Redox/[2 + 2 + 1] Cycloaddition Cascade of Nitroalkyne Substrates

Abstract

We report a new redox/cycloaddition cascade on readily available 1-alkynyl-2-nitrobenzenes that produces complex azacyclic compounds stereoselectively. The core structures of the resulting products are constructed through a formal [2 + 2 + 1] cycloaddition among α-carbonyl carbenoids, nitroso species, and external alkenes.

Gold‐Catalyzed Cyclization/Oxidative [3+2] Cycloadditions of 1,5‐Enynes with Nitrosobenzenes without Additional Oxidants

“…With an increased loading (4 equiv) of 2 a, the yield of 3 a was significantly increased to 82 % (entry 3 . The yield of 5 a was almost the same as that for 3 a according to the NMR analysis of the crude reaction mixture (entries [3][4][5][6]. The oxidative cycloadditions of 2 a (4 equiv) with various 1,5-enynes (1 b-1 i) bearing a variety of alkynyl and phenyl substituents (R, X, and Y) is shown ( Table 2).…”

“…Although catalytic cycloadditions of nitrosobenzenes have been intensively studied, [5,6] we are aware of no report on the cycloaddition of nitroso species with 1,n-enynes (n = 5-7).…”

“…Although catalytic cycloadditions of nitrosobenzenes have been intensively studied, [5,6] we are aware of no report on the cycloaddition of nitroso species with 1,n-enynes (n = 5-7). [6] We report herein the gold-catalyzed cyclization/oxidative [3+2] cycloadditions of 1,5-enynes with nitrosobenzenes. Notably, nitrosobenzenes not only provide two-atom building units, but also lead to the alkyne oxidation.…”

Gold α‐Oxo Carbenoids in Catalysis: Catalytic Oxygen‐Atom Transfer to Alkynes

“…[22] The core structures of 29 are constructed through a formal [2+2+1] cycloaddition between a-carbonyl carbenoids, nitroso species, and external alkenes. A gold a-oxo carbenoid 30 was proposed to be generated from an internal redox process.…”

Isolation of Azomethine Ylides and Their Complexes: Iridium(III)‐Mediated Cyclization of Nitrone Substrates Containing Alkynes

“…[2] This research area is rapidly growing owing to the unique properties of these metals in promoting two or more mechanistically distinct reactions in a tandem process to achieve molecular complexity from simple starting materials. [2] Among the various nucleophiles that are known to attack alkynes, nitrone, [3,4] nitro, [5] sulfoxide, [6] and amine N-oxide [7] groups are particularly interesting. Nucleophilic attack of these polar N + ÀO À groups on alkynes gives metal vinyl species [8] bearing a positively charged electrophilic center (A, Scheme 1; shown for endo cyclization only).…”