Stereoselective Synthesis of 1, 3‐Diaminotruxillic Acid Derivatives: An Advantageous Combination of CH‐ortho‐Palladation and On‐Flow [2+2]‐Photocycloaddition in Microreactors. Issue 1 (24th November 2015)

• Record Type: Journal Article
• Authors: Serrano, Elena; Juan, Alberto; García‐Montero, Angel; Soler, Tatiana; Jiménez‐Márquez, Francisco; Cativiela, Carlos; Gomez, M. Victoria; Urriolabeitia, Esteban P.
• Is Part Of: Chemistry. Volume 22:Issue 1(2016)
• Page Start: 144
• Page End: 152
• Publication Date: 2015-11-24
• Subjects: CH activation -- lactones -- microreactors -- palladium -- photochemistry; Chemistry -- Periodicals; 540
• DOI: 10.1002/chem.201503742
• Languages: English
• ISSNs: 0947-6539

Abstract

Abstract: The stereoselective synthesis of ε‐isomers of dimethyl esters of 1, 3‐diaminotruxillic acid in three steps is reported. The first step is the ortho ‐palladation of ( Z )‐2‐aryl‐4‐aryliden‐5(4 H )‐oxazolones1 to give dinuclear complexes2 with bridging carboxylates. The reaction occurs through regioselective activation of the ortho ‐CH bond of the 4‐arylidene ring in carboxylic acids. The second step is the [2+2]‐photocycloaddition of the CC exocyclic bonds of the oxazolone skeleton in2 to afford the corresponding dinuclear ortho ‐palladated cyclobutanes3 . This key step was performed very efficiently by using LED light sources with different wavelengths (465, 525 or 625 nm) in flow microreactors. The final step involved the depalladation of3 by hydrogenation in methanol to afford the ε‐1, 3‐diaminotruxillic acid derivatives as single isomers. Abstract : An advantageous combination : The stereoselective synthesis of ε‐isomers of dimethyl esters of 1, 3‐diaminotruxillic acid is easily achieved in three steps (see scheme): 1) regioselective CH‐ ortho ‐palladation of ( Z )‐2‐aryl‐4‐aryliden‐5(4 H )‐oxazolones; 2) efficient [2+2]‐photocycloaddition of the CC exocyclic bonds using LED light sources of different wavelengths in continuous flow microreactors; and 3) depalladation by hydrogenation in methanol.