Photoorganocatalytic Aerobic Oxidative Amine Dehydrogenation/Super Acid‐Mediated Pictet‐Spengler Cyclization: Synthesis of cis‐1,3‐Diaryl Tetrahydroisoquinolines

Abstract

Aerobic oxidative dehydrogenation reactions of benzylamines to imines were studied and the efficiencies of various ground‐ and excited state quinone organocatalysts were compared. Long wave‐absorbing anthraquinones readily catalyze the aerobic photodehydrogenation of primary and secondary benzylamines to benzylidenebenzylamines with high rate and selectivity, and the reaction mechanism was studied by laser flash photolysis. Further, branched α‐benzyl dibenzyl‐amines undergo a regioselective photocatalytic dehydrogenation to branched aldimines, which can efficiently be converted into cis‐1,3‐diaryl tetrahydro‐isoquinolines through diastereoselective super acid‐mediated Pictet‐Spengler cyclizations.magnified image

Visible Light-Induced Aerobic Oxidative Dehydrogenation of C–N/C–O to C=N/C=O Bonds Using Metal-Free Photocatalysts: Recent Developments

“…In the first case, the fact that it could be possible to mimic the solar light environment with a sunlight simulator lamp makes the system very attractive, while in the second case carried out under direct real sunlight irradiation, the nanoassemblies have excellent aggregation-induced emission enhancement (AIEE) and intramolecular charge transfer (ICT), characteristics added to their potential to generate ROS. Interestingly, an anthraquinone-based photocatalyst (5), which previously showed excellent activity in the oxidative coupling of benzylamines to N-benzylidene benzylamines 2 [75], has also been used to synthesize cis-1,3-diaryl tetrahydroisoquinolines 7 through a photo-organocatalytic aerobic oxidative amine dehydrogenation/super acidmediated Pictet-Spengler cyclization (Scheme 3) [75]. Thus, α-benzyl dibenzyl-amines were regioselectively converted into the corresponding branched aldimines 6 by aerobic oxidative dehydrogenation under visible light (Scheme 3).…”

“…Photo-organocatalytic synthesis of cis-1,3-diaryl tetrahydroisoquinolines 7 by aerobic oxidative amine dehydrogenation/super acid-mediated Pictet-Spengler cyclization. Interestingly, an anthraquinone-based photocatalyst (5), which previously showed excellent activity in the oxidative coupling of benzylamines to N-benzylidene benzylamines 2 [75], has also been used to synthesize cis-1,3-diaryl tetrahydroisoquinolines 7 through a photo-organocatalytic aerobic oxidative amine dehydrogenation/super acid-mediated Pictet-Spengler cyclization (Scheme 3) [75]. Thus, α-benzyl dibenzyl-amines were regioselectively converted into the corresponding branched aldimines 6 by aerobic oxidative dehydrogenation under visible light (Scheme 3).…”

Photocatalytic Azetidine Synthesis by Aerobic Dehydrogenative [2 + 2] Cycloadditions of Amines with Alkenes

“…Consequently, the 3-methyl-substituted analog 1a and styrene ( 3a ) were chosen as model substrates, and a systematic survey of the reaction conditions was initiated for each individual step as well as the one-pot photocatalytic reaction (Scheme ). For the dehydrogenation 1a → 2a (step 1), we initially screened various anthraquinone dyes, potent organic photooxidants that can mediate hydrogen abstraction, photoelectron transfer, as well as energy-transfer reactions . Further, thioxanthone as well as several iridium­(III) complexes were employed (Table S1).…”