Asymmetric binary-acid catalysis: a diastereo- and enantioselective oxa-Nazarov cyclization-Michael addition of conjugated 1,2-diketones

Abstract

Diastereo- and enantioselective oxa-Nazarov cyclization-Michael addition of conjugated 1,2-diketones was achieved by using an asymmetric binary-acid catalysis with chiral phosphoric acid and FeBr3. The reaction affords the corresponding chiral 3(2H)-furanones...

Cu(OTf)2–Phosphoric Acid-Catalyzed Tandem Oxa-Nazarov Cyclization and Dibromination of Conjugated 1,2-Diketones

“…The mixture was directly loaded onto a silica gel column and eluted with PE/EA (40:1) to give the target product 8 (22.1 mg, 0.054 mmol, 27% yield), and only trace compounds 6 and 7 were obtained. 2,6,tetramethylpiperidin-1yl)oxy)furan-3(2H)-one (8). Prepared according to the reaction procedure above and purified by flash chromatography column with PE/EA (40:1) as the eluent; white solid (11.0 mg, 27% yield), mp 123−124 °C; 1 H NMR (500 MHz, CDCl 3 ) δ 8.21 (d, J = 7.0 Hz, 2H), 7.60 (t, J = 7.0 Hz, 1H), 7.52 (t, J = 7.5 Hz, 2H), 1.79 (s, 3H), 1.61−1.49 (m, 5H), 1.42 (s, 3H), 1,39 (s, 3H), 1.34−1.32 (m, 1H), 1.13 (s, 6H) ppm; 13 C{H} NMR (126 MHz, CDCl 3 ) δ 194.…”

“…Fang and co-workers reported I 2 -catalyzed oxa-Nazarov cyclization-Michael addition cascade between vinyl α- diketones and enones via the Lewis acid-mediated allyl cation II (Scheme A) . Very recently, our group has also developed the asymmetric binary-acid catalysis in the oxa-Nazarov cyclization-Michael addition reaction to give the chiral 3­(2 H )-furanones in good yields and high stereoselectivity (up to >95:5 dr and 96% ee, Scheme B) . Herein, achieving a tandem oxa-Nazarov cyclization and dibromination involving conjugated 1,2-diketones 1 and N- bromosuccinimide (NBS, 2a ) remains elusive, despite the tremendous advances in interrupting the Nazarov cyclization with electrophilic halogenation reagents (Scheme C) .…”

“…4 Very recently, our group has also developed the asymmetric binary-acid catalysis 5 in the oxa-Nazarov cyclization-Michael addition reaction to give the chiral 3(2H)-furanones in good yields and high stereoselectivity (up to >95:5 dr and 96% ee, Scheme 1B). 6 Herein, achieving a tandem oxa-Nazarov cyclization and dibromination involving conjugated 1,2-diketones 1 and N-bromosuccinimide (NBS, 2a) remains elusive, despite the tremendous advances in interrupting the Nazarov cyclization with electrophilic halogenation reagents (Scheme 1C). 7 The reactions exhibit a broad scope under rather mild conditions, giving the corresponding 2,4-dibromo-3(2H)-furanones 3.…”

Rapid Construction of Polycyclic Skeletons via Brønsted-Base-Catalyzed Annulations of Ethylidene 1,3-Indenediones and Vinyl 1,2-Diketones

“…Moreover, in recent years our group and others have been interested in exploring novel reactions using 1,2-diketones . A series of complicated molecules have been rapidly constructed through the regio- and stereoselective transformations.…”

Palladium-Catalyzed Synthesis of Indanone via C–H Annulation Reaction of Aldehydes with Norbornenes

“…Of all the available methods to accomplish indanone-based molecules, the intramolecular Friedel–Crafts acylation and Nazarov cyclization are the most popular methods, which, however, often suffer from some drawbacks including narrow substrate scopes and harsh reaction conditions (Scheme , eq 1). In recent years, various transition metal catalysts such as copper, palladium, and rhodium have been utilized in the synthesis of indanones by using the starting materials of preactivated aldehydes, nitriles, amides, esters, or halides (Scheme , eq 2).…”