Chiral phosphine Lewis base catalyzed asymmetric aza-Baylis-Hillman reaction of N-sulfonated imines with methyl vinyl ketone and phenyl acrylate

In the aza-Baylis-Hillman reaction of N-sulfonated imines with methyl vinyl ketone (MVK) promoted by chiral phosphine Lewis base: (R)-2'-diphenylphosphanyl-[1,1']binaphthalenyl-2-ol (10 mol%), the aza-Baylis-Hillman adducts 1 were obtained in good yields with high ee (70-94% ee) at -30 degrees C in THF. In CH2Cl2 upon heating at 40 degrees C, the aza-Baylis-Hillman reaction of N-sulfonated imines with phenyl acrylate gave the adducts 2 in high yields (60-97%) with moderate ee (52-77%).     

An unexpected highly stereoselective double aza-Baylis-Hillman reaction of sulfonated imines with phenyl vinyl ketone

The aza-Baylis-Hillman reaction of N-sulfonated imine with phenyl vinyl ketone gave the double aza-Baylis-Hillman adduct in good yields with excellent stereoselectivities in the presence of Lewis base 1,4-diazabicyclo[2.2.2]octane.     

Aza-Baylis-Hillman reaction of salicyl N-tosylimines with methyl vinyl ketone, ethyl vinyl ketone or phenyl vinyl ketone

Reactions of salicyl N-tosylimines with methyl vinyl ketone, ethyl vinyl ketone or phenyl vinyl ketone proceeded smoothly under mild conditions to give the corresponding chromanes or aza-Baylis-Hillman adducts in moderate to excellent yields in the presence of phosphine or nitrogen Lewis base.     

Catalytic, asymmetric aza-Baylis-Hillman reaction of N-sulfonated imines with activated olefins by quinidine-derived chiral amines

The chiral nitrogen Lewis base, tricyclic cinchona alkaloid derivative TQO, is an effective promoter in the catalytic, asymmetric aza‐Baylis–Hillman reaction of N‐sulfonated imines Ar? CH?NR′ 1 (R′ = Ts, Ms, Ns, SES) with various activated olefins such as methyl vinyl ketone (MVK), ethyl vinyl ketone (EVK), acrolein, methyl acrylate, phenyl acrylate, or α‐naphthyl acrylate to give the corresponding adducts in moderate to good yields with good to high ee (up to 99 %) at ?30 °C or 45 °C in various solvents, including DMF/MeCN (1:1, v/v). The first such reaction of 1 with the simplest Michael acceptor MVK and methyl acrylate has been achieved with excellent enantioselectivity. The adducts derived from MVK and EVK had the opposite absolute configuration to those from acrolein, methyl acrylate, phenyl acrylate, and α‐naphthyl acrylate. A plausible mechanism has been proposed on the basis of previous reports and the authors’ investigations. An effective bifunctional chiral nitrogen Lewis base–Brønsted acid system has been revealed in this type of aza‐Baylis–Hillman reaction.     

Traditional Morita-Baylis-Hillman reaction of aldehydes with methyl vinyl ketone co-catalyzed by triphenylphosphine and nitrophenol

In the Morita-Baylis-Hillman reaction of aldehydes with methyl vinyl ketone (MVK), we found that in the presence of a catalytic amount of phenol, the Lewis base triphenylphosphine can effectively promote the reaction to give the corresponding normal Morita-Baylis-Hillman adducts in good yields. The mechanism has been investigated by 31P NMR spectroscopy. The solvent and substituent effects were also examined.     

Asymmetric catalytic aza-Morita-Baylis-Hillman reaction using chiral bifunctional phosphine amides as catalysts

The asymmetric catalytic aza-Morita-Baylis-Hillman reaction of N-sulfonated imines with α,β-unsaturated ketones has been successfully conducted by using chiral bifunctional phosphine amides as catalysts. A series of new chiral bifunctional phosphine amides were designed, synthesized, and systematically studied for this asymmetric reaction. The corresponding aza-MBH adducts were obtained in good yields (75-99%) and up to very good enantiomeric excesses (51-95% ee) under mild conditions.     

Highly efficient aza-Baylis-Hillman reaction of N-tosylated imines with MVK, acrolein, and phenyl acrylate or alpha-naphthyl acrylate: Lewis base effects and a convenient method to synthesize alpha,beta-unsaturated beta-amino carbonyl compounds

This paper describes several highly efficient aza-Baylis-Hillman reactions of N-tosylated imines with MVK, acrolein, and phenyl acrylate or alpha-naphthyl acrylate in the presence of a Lewis base. In most cases, the reaction can be completed within 1 h using the appropriate Lewis base catalyst. An efficient method to synthesize beta-amino ketones, aldehydes and esters in high yields and short reaction time has been developed.     

Catalytic,asymmetric aza-Baylis–Hillman reaction of N-sulfonated imines with 2-cyclohexen-1-one and 2-cyclopenten-1-one in the presence of a chiral phosphine Lewis base

In the aza-Baylis–Hillman reaction of N-sulfonated imines with 2-cyclohexen-1-one or 2-cyclopenten-1-one, we found that by using (R)-2′-dimethylphosphanyl-[1,1′]binaphthalenyl-2-ol LB1 as a chiral phosphine Lewis base, the corresponding Baylis–Hillman adducts 2 or 3 can be obtained in good yields and moderate enantiomeric excess. The structure of this chiral phosphine Lewis base on chiral induction in this reaction has also been discussed.     

New multifunctional chiral phosphines and BINOL derivatives co-catalyzed enantioselective aza-Morita-Baylis-Hillman reaction of 5,5-disubstituted cyclopent-2-enone and N-sulfonated imines

New multifunctional chiral phosphine (phosphine-amide type) and BINOL derivative co-catalyzed asymmetric aza-MBH reaction of 5,5-disubstituted cyclopent-2-enones with N-sulfonated imines afforded the corresponding optically active adducts in good to outstanding yields with moderate to good ee's under mild conditions. The steric hindrance environment of BINOL derivatives as well as the nucleophilicity of the phosphorus center and the acidity of free OH which could significantly affect the stereochemical and chemical outcomes had been discussed, indicating the co-catalyzed system is very important to this particular asymmetric aza-MBH reaction.     

An unexpected highly diastereoselective double Baylis-Hillman reaction of per- (or poly)fluorophenyl aromatic aldimines with methyl vinyl ketone

Aza-Baylis-Hillman reaction of per- (or poly)fluorophenyl aromatic aldimines 1 with methyl vinyl ketone (MVK) was studied. It was found that both the used Lewis base and solvent can significantly affect the reaction. Using triphenylphosphine as a Lewis base, the reaction of 1 with MVK proceeded smoothly to give the normal Baylis-Hillman adduct 2 along with the double Baylis-Hillman adduct 3 as by-product in THF. When 1,4-diazabicyclo[2.2.2]octane was used as a Lewis base in DMF, the aza-Baylis-Hillman reaction of 1 with MVK gave the double aza-Baylis-Hillman adduct 3 exclusively in moderate to good yields with excellent diastereoselectivities. The double Baylis-Hillman adduct 3 was conveniently converted to fluorine-containing 4-alkylidene-2-cyclohexen-1-ones under mild reaction conditions in good yields.     

Aza-Baylis-Hillman reactions of diisopropyl azodicarboxylate or diethyl azodicarboxylate with acrylates and acrylonitrile

It has been found that in the Baylis-Hillman reactions of DIAD or DEAD with acrylates or acrylonitrile, the Lewis base and solvent can significantly affect the reaction rate. Using DABCO as Lewis base in DMF or THF, the corresponding aza-Baylis-Hillman adducts 2 or 3 can be obtained in moderate to good yields.     

A catalytic asymmetric strecker-type reaction promoted by Lewis acid-Lewis base bifunctional catalyst

A general asymmetric Strecker-type reaction is reported, catalyzed by the Lewis acid-Lewis base bifunctional catalyst 1. The reaction of trimethylsilyl cyanide (TMSCN) with various fluorenyl imines, including n-aldimines and alpha,beta-unsaturated imines, proceeds with good to excellent enantioselectivities in the presence of a catalytic amount of phenol as additive (20 mol%) (catalytic system 1). The products were successfully converted to the corresponding amino acid derivatives in high yields without loss of enantiomeric purity. Furthermore, hydrogenation or dihydroxylation of the products from alpha,beta-unsaturated imines afforded saturated or functionalized aminonitriles also without loss of enantiomeric purity. The absolute configuration of the products and a control experiment using catalyst 2 supported the proposed dual activation of the imine and TMSCN by the Lewis acid (Al) and the Lewis base moiety (phosphine oxide) of 1. From the mechanistic studies including kinetic and NMR experiments of the catalytic species, the role of PhOH seems to be a proton source to protonate the anionic nitrogen of the intermediate. Specifically, we have found that TMSCN is more reactive than HCN in this catalytic system, probably due to the activation ability of the phosphine oxide moiety of 1 toward TMSCN. This fact prompted us to develop the novel catalytic system 2, consisting of 1 (9 mol%), TMSCN (20 mol%) and HCN (1.2 mol eq). This new system afforded comparable results with obtained by system 1 (1 (9 mol%)-TMSCN (2 mol eq)-PhOH (20 mol%)).     

Reactions of arylaldehydes and N-sulfonated imines with dimethyl acetylenedicarboxylate catalyzed by nitrogen and phosphine lewis bases

[reaction: see text] In the reaction of arylaldehydes or N-sulfonated imines (0.5 mmol) with dimethyl acetylenedicarboxylate (DMAD) (0.6 mmol) catalyzed by pyridine or DMAP (20 mol %), we found that (E)-2-aryl-but-2-enedioic acid dimethyl ester 1 or (E)-2-[aryl-(toluene-4-sulfonylimino)methyl]-but-2-enedioic acid dimethyl ester 2 was formed in good yields at 60 degrees C in THF. A plausible mechanism has been proposed.     

Chiral bifunctional organocatalysts in asymmetric aza-Morita-Baylis-Hillman reactions of ethyl (arylimino)acetates with methyl vinyl ketone and ethyl vinyl ketone

The bifunctional chiral phosphine Lewis base (R)-2'-diphenylphosphino-[1,1'-binaphthalene]-2-ol is an effective organocatalyst in the asymmetric aza-MBH reaction of ethyl (arylimino)acetates 1 with MVK and EVK to give the corresponding adducts in moderate to good yields and good to high enantiomeric excesses under mild conditions.     

Boron（Ⅲ） Tribromide or Tianium （Ⅳ） Bromide and Lewis Base Promoted Baylis—Hillman Reaction

It was found that,when the Baylis-Hillman reaction of arylaldehydes with methyl vinyl ketone was carried out at below -20℃ in the presence of boron (Ⅲ） tribromide or titanium (Ⅳ） bromide using a catalytic amount of Lewis base such as amine,the brominated compounds and the Baylis-Hillman adducts could be obtained as the major products in good yields for various aryl aldehydes.But at room temperature,the elimination products were the major products.In addition,the palladium catalyzed allylic substitution reactions of the elimination products were also examined.     

Chiral phosphine oxide BINAPO as a Lewis base catalyst for asymmetric allylation and aldol reaction of trichlorosilyl compounds

Chiral phosphine oxide BINAPO, which was readily prepared from chiral phosphine BINAP, exhibited good catalytic activities in the reaction of trichlorosilyl compounds via hypervalent silicate intermediates. The allylation of aldehydes with allyltrichlorosilanes in the presence of a catalytic amount of BINAPO gave the allylated adducts in good enantioselectivities (up to 79% ee) wherein a combination of diisopropylethylamine and tetrabutylammonium iodide as additives was crucial to accelerate the catalytic cycle. ³¹P NMR analysis of the phosphine oxide suggested that the amine promoted the dissociation of phosphine oxide from silicon atom. BINAPO also promoted the enantioselective aldol reaction of aldehydes with trichlorosilyl enol ethers in the presence of diisopropylethylamine as an additive to afford the corresponding aldol adducts in high diastereo- and enantioselectivities (up to syn/anti=1/25, 96% ee (anti)).     

A New BINOL-Derived Chiral Bifunctional Phosphine Organocatalyst: Preparation and Application in Asymmetric (Aza)-Morita-Baylis-Hillman Reactions

Abstract

A new BINOL-derived chiral bifunctional phosphine has been designed and successfully prepared, which features a cyclic substructure of 1,3,5-diazaphosphinane. This chiral phosphine possesses good air stability in solid state, and it can be conveniently used as a relatively more nucleophilic phosphine organocatalyst. Preliminary investigations showed that it could generally afford fair to excellent yields but only modest enantioselectivity in the (aza)-Morita–Baylis–Hillman reactions of activated olefins such as ethyl acrylate and methyl vinyl ketone with aldehydes or imines.

[Supplementary materials are available for this article. Go to the publisher's online edition of Phosphorus Sulfer and Silicon and the Related Elements for the following free supplemental files: Additional text and figures.]     

Titanium(IV) chloride and the amine-promoted baylis-hillman reaction

In the Baylis-Hillman reaction, we found that, when the reactions of arylaldehydes with methyl vinyl ketone were carried out at <-20 degrees C using a catalytic amount of amine as a Lewis base in the presence of titanium(IV) chloride, the chlorinated compounds 1 could be obtained as the major product in very high yields for various arylaldehydes. In addition, acrylonitrile could undergo the same reaction to give the corresponding chlorinated product in moderate yield.     

Aza-Baylis-Hillman reactions of N-tosylated aldimines with activated allenes and alkynes in the presence of various Lewis base promoters

[reaction: see text] The attempted aza-Baylis-Hillman reactions of N-tosylated aldimines with ethyl 2,3-butadienoate, ethyl penta-2,3-dienoate, penta-3,4-dien-2-one, methyl propiolate, and but-3-yn-2-one have been systematically investigated in the presence of various nitrogen or phosphine Lewis base promoters. We found that a series of nitrogen-containing heterocyclic compounds, as "abnormal" aza-Baylis-Hillman reaction products, can be formed in the presence of an appropriate Lewis base promoter. The Lewis base and solvent effects in these reactions have been discussed along with the corresponding plausible mechanism.     

Catalytic enantioselective aza-Diels-alder reactions of imines--an approach to optically active nonproteinogenic alpha-amino acids

A catalytic enantioselective aza-Diels-Alder reaction of imines has been developed. The reaction of N-tosyl alpha-imino ester with different dienes including activated, non-activated, cyclic, and acyclic dienes has been investigated in the presence of various chiral Lewis acids. A series of phosphino-oxazoline ligands have been synthesized and evaluated for the reaction. It was found that the combination of phosphino-oxazoline ligands with copper(I) salts gives the best results for the activated dienes, while BINAP-copper(I) complexes are good catalysts for all the dienes studied. In the case of activated acyclic dienes the aza-Diels-Alder products can be obtained in higher than 80% isolated yield and 96% ee, while for the unactivated cyclic dienes the exo diastereomer is formed as the major product in up to 95 % ee. For an activated cyclic conjugated diene, 2-trimethylsilyloxy-1,3-cyclohexadiene, the reaction proceeds as a Mannich-type addition reaction giving optically active gamma-oxo alpha-amino acid derivatives in good yields and up to 96% ee. The reaction of an unactivated acyclic diene, 2,3-dimethyl-1,3-butadiene, with the N-tosyl alpha-imino ester gives both the aza-Diels-Alder and aza-ene products, in a ratio of 9:1 favoring the aza-Diels-Alder product. Furthermore, a series of different imines have been synthesized and investigated as possible substrates for the present catalytic enantioselective aza-Diels-Alder reaction in order to obtain mechanistic insight. All imines studied gave moderate to high ee. Particularly, the reaction of the N-phenyl and N-p-methoxyphenyl substituted glyoxylate imines with Danishefsky's diene proceeded well affording the corresponding aza-Diels-Alder product in high yield with up to 91% ee at room temperature. The present catalytic enantioselective reaction of imines provided an effective route to optically active nonproteinogenic alpha-amino acids. The products of the catalytic enantioselective aza-Diels-Alder reaction of the cyclic dienes can be used for the preparation of key compounds such as natural products and compounds of pharmaceutical interest. The absolute configurations of five products have been solved by X-ray structural analysis, and it is found that the absolute configuration of the aza-Diels-Alder adduct is dependent on the substituent on the imine nitrogen atom. It turned out that the N-tosyl glyoxylate imine and N-p-methoxyphenyl glyoxylate imine give the aza-Diels-Alder adduct with opposite absolute configuration using the same enantiomer of the catalyst. On the basis of the results the mechanistic aspects for the reactions are discussed.