One Step Synthesis of Chiral Olefins via Asymmetric Diamination and their Applications as Ligands for Rhodium(I)‐Catalyzed 1,4‐Additions

Abstract

A variety of acyclic chiral dienes were synthesized in a single step via palladium(0)-catalyzed asymmetric allylic and homoallylic C À H di-A C H T U N G T R E N N U N G amination of terminal olefins. The applications of such simple dienes as steering ligands for rhodi-A C H T U N G T R E N N U N G um(I)-catalyzed asymmetric 1,4-additions afforded the corresponding adducts in excellent yields and up to 85% ee.Keywords: acyclic chiral dienes; asymmetric catalysis; asymmetric diamination; conjugated addition; diene ligands Chiral olefins have proven to be excellent steering ligands for asymmetric catalysis, and some of them even exhibit a distinct advantage over other types of ligands to afford higher reactivities and/or enantioselectivities. [1,2] With lots of effort devoted to this lately emerging area, a few fantastic chiral chelating diene ligands bearing bicyclic frameworks have been successfully developed. [3][4][5][6] The bicyclic structures of these ligands play a crucial role in the asymmetric reactions, but also partially result in some difficulties in ligand synthesis. Hence, exploring novel, effective, and accessible chiral dienes is still one of the most important subjects in this field.[2b] Inspired by the fact that 1,5-hexadiene (1) has an ability to act as a steering ligand, very recently, we reported that a simple chiral acyclic diene 2 (Scheme 1) can be employed as an effective ligand for promoting Rh(I)-catalyzed asymmetric 1,4-additons with encouraging yields and ees (Scheme 2), [7,8] which demonstrates that the complexes formed between Rh and a flexible diene are stable enough to ensure asymmetric induction.[9] Because of the convenient synthesis, chiral acyclic dienes have the potential to become a class of promising ligands in the future. Herein, we wish to report our efforts on this subject.In our previous work, when two hydroxy groups were introduced into the achiral 1,5-hexadiene skeleton, a simple chiral chain diene ligand 2 was successfully achieved, which suggests that other types of chiral dienes containing 1,5-hexadiene skeletons are also candidate ligands. We envisioned that introduction of imidazolidin-2-one backbones to 1,5-hexadiene may provide a good opportunity to develop novel diene ligands (3) for asymmetric catalysis (Scheme 1).[10] The combination of flexible terminal olefins and rigid imidazolidin-2-one frameworks in ligand 3 and how it might affect asymmetric induction is interesting. Therefore, building the chiral imidazolidin-2-one frameworks became one of the key points.

Rh-catalyzed asymmetric 1,4-addition reactions to α,β-unsaturated carbonyl and related compounds: an update

“…Notably, the enantioselectivities were also very high for arylmethylene cyanoacetates where the aryl groups were 2-methylphenyl, 2-naphthyl, and 4-chlorophenyl (Table 39). 141 A highly stereoselective synthesis has been reported by the chiral diene/rhodium-catalyzed stereoselective 1,4-addition of arylboronic acids 2 to b-aryl-substituted a,b-unsaturated aldehydes and esters 1u,v, which gave the corresponding b,b-diaryl substituted products 145a, b with 90-93% ee 142-144 (Scheme 56).…”

Synthesis of Chiral Olefin Ligands and their Application in Asymmetric Catalysis

“…In 2009, Du and co-workers found that 1,5-hexadiene can act as an effective ligand for Rh I -catalyzed 1,4-addition of phenylboronic acid (25 a) to 2-cyclohexenone (24 a) to give the corresponding adduct 26 a with quantitative conversion (Scheme 4). [25] Inspired by this experimental result, the known compound (3R,4R)-hexa-1,5-diene-3,4-diol (27) was also used as a ligand for this reaction. Significantly, with the use of such a simple diene ligand bearing just two terminal olefins, the desired product 26 a was obtained in 98 % yield with 82 % ee (Scheme 4).…”

“…[18] Recent studies on chiralchain diene ligands have demonstrated that two simple terminal olefin moieties can ensure satisfactory activity and selectivity. [25,27,28,[30][31][32] Therefore, the combination of terminal olefins and a phosphorus atom, which gives stronger coordination ability, on suitable chiral frameworks possibly provides a practical strategy for developing novel P/olefin hybrid ligands.…”

“…[25] Subsequently, Du and co-workers used a diamination method developed by Shi and co-workers [26] for the synthesis of chain dienes containing chiral imidazolin-2-one frameworks. [27] Enantiomerically pure diene 30 was easily obtained in only one step through a Pd-catalyzed diamination of 1,5-hexadiene with di-tert-butyldiazridinone (28) as the nitrogen source and chiral phosphoramidite ligand 29, with subsequent recrystallization in hexanes (Scheme 5). Similar dienes 31 were also available by using various 1,5-dienes as substrates.…”

Gold(I)‐Catalyzed Intramolecular Hydroamination of N‐Allylic N′‐Arylureas to form Imidazolidin‐2‐ones

“…[7] Furthermore, chiral, non-racemic imidazolidin-2-ones have been employed as chiral auxiliaries [8,9] and as scaffolds for bis(phosphine) ligands [10,11] for use in enantioselective synthesis. A number of approaches to construction of the imidazolidin-2-one ring have been developed [12–20] including carbonylation of vicinal diamines, [13] oxidative diamination of alkenes with ureas, [14,15] and electrophilic cyclization [16] or transition metal-catalyzed carboamination of N -allylic ureas. [17,18] In contrast, transition metal-catalyzed alkene hydroamination, which represents perhaps the most conceptually simple and atom-economical approach to the cyclization of readily available N -allylic ureas, has gone largely unexplored as a route to the imidazolidin-2-one ring.…”