Practical metal-free synthesis of chalcone derivatives via a tandem cross-dehydrogenative-coupling/elimination reaction

Abstract

Metal-free synthesis of chalcone derivatives through a tandem cross-dehydrogenative-coupling/elimination reaction is described. A simple and inexpensive ammonium persulfate salt enables the reaction between ketones and benzylamines to proceed with high stereoselectivity and good functional group compatibility.a Reaction conditions: propiophenone 1a (0.5 mmol), benzylamines 2 (2.5 mmol), (NH 4 ) 2 S 2 O 8 (1.5 mmol) in tert-amyl-OH (1.0 mL) at 120 °C for 24 h. b 1 H NMR yield using tetrachloroethane as an internal standard. c Isolated yield in parentheses for the 1.0 g scale synthesis. † Electronic supplementary information (ESI) available: Experimental procedures and product characterization. See

Metal-free one-pot synthesis of 2-substituted and 2,3-disubstituted morpholines from aziridines

“…To our delight, NMR studies showed that chloroethoxyamine 2a is observed as the only ring-opening product. After screening different persulfates, in concordance with Zeng [ 32 ], we found that ammonium persulfate ((NH 4 ) 2 S 2 O 8 ) is superior to Na 2 S 2 O 8 and K 2 S 2 O 8 in the transformation, leading to chloroethoxyamine 2a in an excellent yield (93%) in short time.…”

“…Based on the above results, a viable mechanism was proposed as shown in Scheme 4 . Initially, aziridine 1a might participate in single-electron transfer (SET) with the persulfate anion to render the radical cation A [ 32 , 34 ]. Concerted ring opening and nucleophilic addition leads to amino radical intermediate B , which is converted to the haloalkoxy amine intermediate 2a after abstraction of one hydrogen atom from alcohol.…”

“…Recently we have reported the visible light-mediated ring opening of aziridines by a number of nucleophiles, such as LiBr, NaN 3 and alcohols [ 24 ]. As a part of an ongoing program on the ring opening of aziridines [ 25 – 31 ], we have developed an efficient method for the synthesis of 2-substituted and 2,3-disubstituted morpholines from aziridines utilizing a simple and inexpensive ammonium persulfate salt as the oxidant at room temperature ( Scheme 1 ) [ 32 – 33 ].…”

Oxidative Olefination of Benzylamine with an Active Methylene Compound Mediated by Hypervalent Iodine (III)

“…So far there are only two reports available for the oxidative olefination of amines. In 2013, X. Zeng and co‐worker report oxidative olefination of N ‐methyl benzylamines with carbon nucleophiles such as acetophenone by using stoichiometric amount (NH 4 ) 2 S 2 O 8 (Scheme ) . In the same year, Tian and co‐workers described the oxidative olefination of N ‐phenyl benzylamines with carbon nucleophiles such as 2‐ and 4‐methyl pyridine, quinoline, isoquinoline, malononitrile as substrate by using stoichiometric amount of DDQ …”

Palladium‐Catalysed Cross‐Coupling Reactions for the Synthesis of Chalcones

“…It is noteworthy to mention that other uncommon reactions such as the Friedel‐Crafts alkylation, Knoevenagel condensation, and Julia‐Kocienski have also been explored and studied. Other atypical reactions including the olefin cross‐metathesis reaction, the silver‐catalysed double‐decarboxylative cross coupling, bio‐derived ZnO nanoflower and the green metal‐free synthesis via a tandem cross‐dehydrogenative coupling/elimination reaction have also been reported. Propargyl alcohol derivatives have also been used as precursors for isomerization reaction or through the Meyer‐Schuster rearrangement to produce the corresponding enones.…”