Enantioselective aza-Diels–Alder reaction of Brassard’s diene with aldimines catalyzed by chiral N,N′-dioxide–Yb(OTf)3 complex

Recent applications of rare-earth metal(III) triflates in cycloaddition and cyclization reactions

“…A catalytic enantioselective aza-Diels-Alder reaction of Brassard's diene 51 with aldimines 52 was reported. 48 In contrast with Danishefsky's diene, a double substitution in Brassard's diene terminus hindered the enantioselectivity of the hetero-Diels-Alder reaction under standard conditions. Gratifyingly, a complex of previously mentioned N,N′-dioxide 32 with Yb(OTf) 3 afforded the corresponding α,β-unsaturated γ-lactone derivatives 54 in a two-step process via a Mannich product 53 with moderate to good yields and good enantioselectivities (Scheme 13).…”

Catalytic Asymmetric Aza‐Diels‐Alder Reaction: Pivotal Milestones and Recent Applications to Synthesis of Nitrogen‐Containing Heterocycles

“…Feng and co‐workers [55,56] found that scandium‐ or ytterbium complexes with proline‐derived chiral N , N ′‐dioxide ligands Va and Vb catalyze enantioselectively the NED aza‐DAR of aldimines 4 a with Danishefsky ( 5 b ) or Brassard ( 11 ) dienes. A variety of aromatic, heteroaromatic and aliphatic aldimines are suitable substrates to afford 2,5‐disubstituted dihydropyridinones 6 or 12 in moderate to high yield with up to 90% ee .…”

An enantiodivergent synthesis of Cα-methyl nipecotic acid analogues from δ-lactam derivatives obtained through a highly stereoselective cyclization strategy

“…1 H-NMR (CDCl3, 400 MHz): δ 7.33 (m, 5H), 5.35 (m, 2H), 3.76 (s, 3H), 3.42 (m, 2H), 2.30 (m, 1H), 1.92 (m, 3H), 1.75 (s, 3H). 13…”

“…Recently a number of synthetic strategies have been established to prepare δ-lactams. Some of these strategies include Nheterocyclic catalyzed intramolecular amidations, 11 palladium catalyzed intramolecular amidations, 12 aza-Diels-Alder reactions, 13 intramolecular lactone-amine coupling, 4 gold catalyzed intramolecular C-C couplings of β-ketoamide to unactivated alkenes, 14 and palladium catalyzed intramolecular hydroamidations of alkynes. 15 There have also been several methods detailing the enantioselective synthesis of δ-lactams through ring closing metathesis reactions of enantiomerically pure precursors, 16 nitrilase catalyzed ring expansion of aziridines, 17 and the use of organophosphorus reagents as organocatalysts.…”

“…IR (cm -1 ) = 3219.6, 2940.4, 2871.9, 1726.5, 1655.5. 1 H-NMR (CDCl3, 400 MHz): 7.29 (m, 5H), 5.0 (d, 1H, J = 14.24 Hz), 4.2 (m, 3H), 3.24 (m, 2H), 2.23 (m, 1H), 1.79 (m, 3H), 1.54 (s, 3H), 1.29 (t, 3H, J = 7 Hz) 13. C-NMR (CDCl3, 100 MHz): δ 173.6, 169.3, 137.2, 128.5, 127.8, 127.3, 61.4, 50.7, 50.4, 47.3, 33.4, 22.7, 19.4, 14.2.…”