Methods for the synthesis of chiral sulfur heterocycles and their application in the asymmetric Baylis–Hillman reactions

Enantiomerically pure (2S,6S)-2,6-diphenyltetrahydro-2H-thiopyran, (2S)-2-phenyltetrahydro thiophene, and (2S)-2-phenyltetrahydro-2H-thiopyran were prepared in 70–72% yields and with 86–99% ee via cyclization of the corresponding dimesylate in an S_N2 cyclization reaction using sodium sulfide nonahydrate. The results on the application of various chiral sulfides in asymmetric Baylis–Hillman reactions are also described.     

Morita–Baylis–Hillman reactions of isatins with allenoates

4-(N,N-dimethylamino)pyridine (DMAP) was found to be a fairly efficient catalyst for the Morita–Baylis–Hillman reactions of isatins with α-substituted allenoates to give the corresponding products in good to high yields with moderate diastereoselectivities under mild conditions.     

Facile synthesis of bisphosphine monoxides from Morita–Baylis–Hillman carbonates

A facile two-step synthesis of bisphosphine monoxides (BPMOs, with both the phosphine and phosphine oxide moieties within one molecule) from readily available Morita–Baylis–Hillman (MBH) carbonates was realized. Under the catalysis of DABCO, the MBH carbonates undergo allylic phosphorylation reaction with diphenylphosphine oxide or diethyl phosphonate to give monophosphine oxides bearing an activated alkene moiety; subsequent base-catalyzed hydrophosphination of the prepared monophosphine oxide with HPPh₂ readily affords the BPMOs.     

Amination of the Baylis–Hillman Acetates in Ethanol

Baylis–Hillman acetates in EtOH were substituted by various nitrogen nucleophiles to give the corresponding trisubstituted alkenes in high yields.     

Facile synthesis of γ-alkylidenebutenolides from Morita–Baylis–Hillman adducts

An expedient synthetic procedure of γ-alkylidenebutenolides was developed via a sequential indium-mediated Barbier-type reaction of Morita–Baylis–Hillman bromide with aldehyde, lactonization, and double-bond isomerization. Various γ-alkylidenebutenolides including bovolide and its derivatives were synthesized in good overall yields.     

Acid–base organocatalysts for the aza-Morita–Baylis–Hillman reaction of nitroalkenes

A new class of acid–base chiral organocatalysts 1a and 2 for aza-Morita–Baylis–Hillman (aza-MBH) reaction of conjugated nitroalkenes is described. The acidic phenolic hydroxy groups and basic imidazole unit cooperatively activate nitroalkenes to promote the aza-MBH reaction in good yields with moderate enantioselectivities.     

A new application of Baylis–Hillman alcohols to a diastereoselective synthesis of 3-nitrothietanes

Three key reactions, the generation of a nucleophile, an thia-Michael addition and an intramolecular cyclisation, were used to achieve an efficient one-pot diastereoseletive synthesis of 3-nitrothietanes. Thus, Baylis–Hillman alcohols and their aldehydes were reacted with either O,O-diethyl hydrogen phosphorodithioate or O,O-diethyl hydrogen phosphorodithioate in combination with a task-specific ionic liquid [bmim]X–Y to afford the corresponding 2,3-di- or 2,3,4-trisubstituted thietanes, respectively. The reaction is high yielding and proceeds with complete diastereoselectivity in favour of the trans isomers.     

An expeditious protocol for synthesis of Baylis–Hillman derived piperazine derivatives and evaluation of their AChE inhibition

Research on Chemical Intermediates - The highly efficient and eco-economical “on water” method has been developed for the rapid construction of highly functionalized...     

Efficient synthesis of N-allylated 2-nitroiminoimidazolidine analogues from Baylis–Hillman bromides

Various Baylis–Hillman–derived new N-allylated 2-nitroiminoimidazolidine analogs were efficiently prepared using potassium carbonate as base. Simple workup procedure, excellent yields, and mild reaction conditions are the salient features of this method. All the synthesized compounds are screened for their larvicidal activity on fourth instar mosquito larvae, Culex quinquefasciatus.     

l-proline and l-histidine co-catalyzed Baylis–Hillman reaction

Baylis–Hillman reaction between an aldehyde and an activated alkene, such as alkyl vinyl ketones, acrylates, acrylonitrile, and vinylsulfones, giving the β-hydroxy-α-methylene carbonyl compounds, is a versatile and atom-economical carbon–carbon bond-forming reaction. This reaction usually is catalyzed by strong Lewis bases such as tertiary amines and suffers from slow reaction rate. In this paper the Baylis–Hillman reaction between arylaldehydes and methyl vinyl ketone was successfully realized by a catalytic amount of l-proline and l-histidine system to give the corresponding normal Baylis–Hillman adducts in moderate to high yields for the first time. The effects of solvent and reagent electro property on the yields of this reaction were also investigated. Proline and histidine are naturally widely present amino acids in food system; furthermore, aldehydes and activated alkenes can also be easily produced in food processing, so proline and histidine co-catalyzed Baylis–Hillman reaction may find application in explaining some phenomena in food processing.     

Lipase-catalyzed kinetic resolution of Baylis–Hillman products

Lipase-catalyzed kinetic resolution of the various Baylis–Hillman products, α-methylene-β-hydroxy compounds, were examined. When lipase PS was used as a biocatalyst in acetonitrile, transesterification of racemic ethyl 3-hydroxy-2-methylenebutanoate or 3-hydroxy-2-methylenepentanoate proceeded in a practical enantiomeric excess. The resolution by hydrolysis of the acetate derivatives was also tried. In contrast, in case of racemic ethyl 3-acetoxy-2-methylenepentanoate, under the conditions using lipase AK, the E value of the resolution was >321.     

Synthesis of functionalized and fused furans and pyrans from the Morita–Baylis–Hillman acetates of nitroalkenes

The Morita–Baylis–Hillman (MBH) acetates derived from nitroalkenes and ethyl glyoxylate have been transformed in one pot at room temperature to highly fused and functionalized furans and pyrans in good to excellent yield. The reaction involves a cascade Michael–oxa-Michael addition of β-dicarbonyl compounds to the MBH acetates in the presence of an amine base such as DABCO. An unusual switching of selectivity in the oxa-Michael addition from 5-exo-trig to 6-endo-trig was observed when the β-dicarbonyl compound was changed from acyclic or six-membered ring cyclic to five-membered ring cyclic system.     

Et3B-mediated palladium-catalyzed direct allylic substitution reactions of Morita–Baylis–Hillman alcohols with aromatic amines

An efficient, direct allylic amination of both cyclic and acyclic Morita–Baylis–Hillman alcohols with aromatic amines, in tetrahydrofuran (THF) at room temperature, catalyzed by Pd(0)/Et₃B, is reported herein. The corresponding amines are obtained with a high α -regioselectivity in 65–87% yields.     

Diastereoselective peroxidation of derivatives of Baylis–Hillman adducts

Cyclic derivatives of Baylis–Hillman adducts were synthesized. Cobalt-catalyzed peroxidation of these cyclic lactones afforded silyl peroxides in diastereomeric ratios ranging from 91:9 to 97:3.     

Baylis–Hillman reaction based flexible strategy for the synthesis of gabosine I,gabosine G,epi-gabosine I and carba l-pentose

A combination of diastereoselective Baylis–Hillman reaction and RCM reaction set is used as the flexible strategy for the ready access to cyclohexenoid and cyclopentenoid skeletons.     

1,1′-Carbonyldiimidazole mediates the synthesis of N-substituted imidazole derivatives from Morita–Baylis–Hillman adducts

In this Letter, we describe a simple and straightforward method for the synthesis of N-substituted imidazole derivatives. 1,1-carbonyldiimidazole mediates the process, which requires no activation group step. We obtained imidazole derivatives in high yields and with short reaction times. To demonstrate the synthetic significance of the aforementioned compounds, we also describe the synthesis of novel ionic liquids from these derivatives.     

Asymmetric Morita–Baylis–Hillman reaction of chiral glyoxylates

The first Morita–Baylis–Hillman reaction of chiral glyoxylic acid derivatives, i.e. N-glyoxyloyl-(2R)-bornane-10,2-sultam and (−)-8-phenylmenthyl glyoxylate is described. The reaction with cyclic α,β-unsaturated ketones proceeded under the catalytic influence of dimethyl sulfide in the presence of titanium tetrachloride. The adducts were obtained with very high diastereoisomeric excess (over 95% d.e.) and typical yields of 78%. The absolute configuration of the newly created stereogenic center was established by X-ray crystallographic analysis.     

Aza-Morita–Baylis–Hillman reaction with ion-supported Ph3P

Various N-tosyl arylimines reacted with methyl vinyl ketone and ethyl vinyl ketone in the presence of ion-supported Ph₃P A and B to give adducts, N-(2′-methylene-3′-oxo-1′-arylbutyl)-4-methylbenzenesulfonamides and N-(2′-methylene-3′-oxo-1′-arylpentyl)-4-methylbenzenesulfonamides, respectively, in good yields with high purity by simple diethyl ether extraction of the reaction mixture. Moreover, ion-supported Ph₃P A and B could be repeatedly used for the same reaction to provide the corresponding adducts while maintaining good yields with high purity.     

Chiral phosphine-catalyzed regio- and enantioselective allylic amination of Morita–Baylis–Hillman acetates

Enantioselective allylic substitution of Morita–Baylis–Hillman (MBH) acetates with phthalimide was realized in the presence of a novel l-proline-derived chiral trifunctional phosphine amide ligand to give the corresponding allylic amination adducts in good yields (70–95%) and in modest to good enantioselectivities (34–78% ee’s).     

Simple and New Protocol for the Synthesis of Novel (z)-3-Arylidenebenzothiazepin-4-ones Using Baylis–Hillman Derivatives

A simple synthesis of novel (Z)-3-arylidene-2,3-dihydrobenzo[b][1,4]thiazepin-4(5H)-ones from bromo compounds derived from Baylis–Hillman adducts involving selective S-alkylation followed by a lactum formation has been described.