Reaction of azides and enolisable aldehydes under the catalysis of organic bases and Cinchona based quaternary ammonium salts

Abstract

Herein we report a two-step sequence for the preparation of amides starting from azides and enolisable aldehydes. The reaction proceeded via the formation of triazoline intermediates that were converted into amides via Lewis acid catalysis. Preliminary studies on the preparation of triazolines under chiral phase transfer catalysis are also presented, demonstrating that enantioenriched amides could be prepared from achiral aldehydes in moderate to low enantioselectivity.

Natural and Synthetic Halogenated Amino Acids—Structural and Bioactive Features in Antimicrobial Peptides and Peptidomimetics

“…The racemic preparation of amino acid ( 24 ) has been recently reported on a large scale ( Scheme 2 ). Starting from acidic aminomalonate derivative ( 34 ), its reaction with alkyl chloride ( 35 ) under phase transfer catalysis [ 107 , 108 , 109 , 110 , 111 , 112 , 113 , 114 ] operated by tetrabutylammonium bromide (TBAB) in the presence of catalytic potassium iodide, generated adduct ( 36 ). Hydrolysis and acidic condition promoted decarboxylation and provided compound ( 24 ) as a racemate.…”

Study of Ground State Interactions of Enantiopure Chiral Quaternary Ammonium Salts and Amides, Nitroalkanes, Nitroalkenes, Esters, Heterocycles, Ketones and Fluoroamides

“…The groups of Umani‐Ronchi, [21] Ricci and Bernardi, [22–26] Jørgensen, [27,28] Della Sala [29] and Albanese [30,31] provided notable synthetic applications of Cinchona derived ammonium species. Adamo and coworkers have reported some highly enantioselective reactions that make use of Cinchona ‐based quaternary ammonium salts [32–41] . Concomitantly, the groups of Waser and Vetticatt have reported the use of bifunctional quaternary ammonium salts in highly enantioselective α ‐fluorinations; [42] asymmetric cascade cyclizations; [43,44] Michael additions; [43] α‐ hydroxylations; [45] and α‐ chlorinations [46] …”

“…Adamo and coworkers have reported some highly enantioselective reactions that make use of Cinchona ‐based quaternary ammonium salts. [ 32 , 33 , 34 , 35 , 36 , 37 , 38 , 39 , 40 , 41 ] Concomitantly, the groups of Waser and Vetticatt have reported the use of bifunctional quaternary ammonium salts in highly enantioselective α ‐fluorinations; [42] asymmetric cascade cyclizations;[ 43 , 44 ] Michael additions; [43] α‐ hydroxylations; [45] and α‐ chlorinations. [46] …”

Enantioselective Synthesis of 3,4-Dihydropyran-2-ones via Phase-Transfer-Catalyzed Addition–Cyclization of Acetylacetone to Cinnamic Thioesters

“…We then considered using chiral phase-transfer catalysis to impart an enantioselective outcome to this reaction. Our research group has recently described some highly enantioselective Michael-initiated cyclization reactions (MICRs), which proceed in the presence of chiral Cinchona -derived quaternary ammonium salts. − Salts of quininium/cinchonidinium 4 , quinidinium 5 , and dihydroquinidinium 6 can be easily prepared in a single step by quaternization of cheap, commercially available Cinchona alkaloids with a variety of alkylating agents. − Cinchona alkaloids are convenient materials for organocatalysis and have been preferred to other classes of chiral ammonium salts, which require longer syntheses . With this in mind, we screened a range of Cinchona -derived PTCs 4a – 4g , 5a – 5b , and 6 (Table ) in the model reaction of cinnamic thioester 1a and acetylacetone 2 .…”