Asymmetric Aza-Claisen Rearrangement between Enantioenriched α-Chiral Allylamines and Allenones

Abstract

An unprecedented asymmetric aza-Claisen rearrangement between enantioenriched α-chiral allylamines and allenones was found to proceed in the absence of catalysts and additives at room temperature. The rearrangement, followed by hydrolysis, provides convenient access to structurally diverse δ-chiral β-diketones in good to excellent yields with excellent retention of enantiopurity. This protocol proved powerful for the construction of an all-carbon quaternary stereocenter with high enantiopurity.

Cobalt-catalyzed regioselective hydroazidation of 1-aryl-1,3-dienes: facile access to allylic azides

“…Finally, several other H sources were investigated for the reaction in chloroform using Co (salen) C2 (6 mol%) as the catalyst and N-fluorobenzenesulfonimide (NFSI) as the oxidant. Only 21% yield was obtained using PhMeSiH 2 (Table 1, entry 13), while other H-sources including Et 3 SiH, PhMe 2 SiH, and PhSiH 3 did not promote the reaction effectively (Table 1, entries [14][15][16]. When reducing the dosage of TMSN 3 from 1.0 mmol to 0.75 mmol, the yield decreased to 54% (Table 1, entry 17, standard conditions).…”

“…14 Subsequently, 3ga underwent a substitution reaction with 1,4-dibromobutane at 110 °C to afford (E)-1-(4-([1,1′-biphenyl]-4-yl)but-3-en-2-yl)pyrrolidine (3gb) in 70% yield (Scheme 4). 15 To gain some insights into the mechanism of this transformation, 2,2,6,6-tetramethyl-1-piperidinyloxy (TEMPO) as a radical scavenger was added to the model reaction, and the formation of 3a was inhibited. The allyl radical was trapped and gave product 3u in a yield of 46% (Scheme 5).…”

“…14 Subsequently, 3ga underwent a substitution reaction with 1,4-dibromobutane at 110 °C to afford ( E )-1-(4-([1,1′-biphenyl]-4-yl)but-3-en-2-yl)pyrrolidine ( 3gb ) in 70% yield (Scheme 4). 15…”

Modular Synthesis of Enantioenriched α-Chiral Homoallylic Amidines Enabled by Relay Ir/Cu Catalysis

“…The Claisen rearrangement reaction provides a potentially useful synthetic tool for synthesizing α- or β-chiral homoallyl carbonyl derivatives . In particular, the zwitterionic aza-Claisen rearrangements have been received increased attention because they can proceed under relatively mild conditions after the nucleophilic addition of tertiary allylamines to π-electrophiles (e.g., 2-alkynoates, acetylenic sulfones, allenoates, ketenes, , ketenimines, carbodiimides, isocyanates, isothiocyanates, and so on). Although the stereochemical outcomes of aza-Claisen rearrangements can be expected because of their chairlike six-membered transition states, only a few asymmetric zwitterionic aza-Claisen rearrangements involving allenoates , and ketenes ,,, have been achieved in an enantioselective or stereospecific manner.…”

Gold(I)-Catalyzed Cyclization–3-Aza-Cope–Mannich Cascade and Its Application to the Synthesis of Cephalotaxine

“…The success of this reaction initiated our study into new cascade reactions involving in situ generated vinylammoniums. The intramolecular addition of tertiary amines to alkynes, arynes, allenes, or ketimines is a good method for generating vinylammoniums, and such intermediates have been used to synthesize nitrogen macrocycles through 3-aza-Cope rearrangements . Gold­(I) catalysts operate as soft Lewis acids that can activate alkynes for addition reactions with primary or secondary amines providing cyclic enamines, and vinylammonium intermediates have been proposed in the gold­(I)-catalyzed reactions of aziridines or sulfonamides .…”