Gold(I)‐catalyzed synthesis of dihydrodibenzoquinolizinium salts

Abstract

A gold‐catalyzed cyclization of 1‐alkynyl‐2‐aryl tetrahydroisoquinolines is described for the synthesis of novel dihydrodibenzoquinolizinium salts. The reaction mechanism is likely to involve a 6‐endo‐dig cyclization and subsequent oxidation by air to give a relatively stable arylgold intermediate. This gold species undergoes protodeauration under acidic conditions to afford the title compounds. An NMR study was performed to gain further evidence and insight on the presence of the arylgold intermediate and the reaction mechanism.magnified image

Stereoselective synthesis of 2-spirocyclopropyl-indolin-3-ones through cyclopropanation of aza-aurones with tosylhydrazones

“…[5][6][7][8] However, aza-aurones are also known as powerful synthetic building blocks for cycloaddition reactions both as heterocyclic dienes, furnishing a "four-atom" unit, [9][10][11][12] or by reacting at the exocyclic double bond, providing an easy access to 3-oxo-2spiroannulated indolines (spiropseudoindoxyls) by [n+2] processes. 13,14 (Figure 1).…”

Homogeneous Gold-Catalyzed Oxidation Reactions

“…The proposed mechanism entails gold-catalyzed 6- endo - dig cyclization followed by air oxidation to produce the observed product. In 2017, G. Verniest reported a synthetic route to dihydrodibenzoquinolizinium salt 196 from 1-alkylcinoline 195 (Scheme C) . The reaction is catalyzed by in situ -generated Ph 3 PAuNTf 2 at ambient temperature, requires stoichiometric MsOH, and works with either an aromatic or alkyl substituent at the alkyne terminus.…”

“…In 2017, G. Verniest reported a synthetic route to dihydrodibenzoquinolizinium salt 196 from 1-alkylcinoline 195 (Scheme 111C). 273 The reaction is catalyzed by in situgenerated Ph 3 PAuNTf 2 at ambient temperature, requires stoichiometric MsOH, and works with either an aromatic or alkyl substituent at the alkyne terminus. Interestingly, quinolinium intermediate HM is isolable and can undergo protodeauration in the presence of trifluoracetic acid to afford the final product.…”

Gold-Catalyzed Reactions of Specially Activated Alkynes, Allenes, and Alkenes

“…Quinolinium salts are also accessible by a Au-catalyzed hydroarylation of an electron deficient alkynyl ester as shown by Verniest and Marien (Scheme 127). 225 While the transformation developed by the authors was mainly applied to nonspecially activated alkynes, the single example featuring the cyclization of 550 into 551 could most probably be applied to other carbonyl substituted alkynes. Interestingly, the reaction was performed in the presence of an acid to favor the protodeauration step and disfavor the coordination of the gold complex onto the nitrogen atom of the aniline moiety.…”