Allylation Reactions of Aldehydes with Allylboronates in Aqueous Media: Unique Reactivity and Selectivity that are Only Observed in the Presence of Water

Zn(OH)₂‐catalyzed allylation reactions of aldehydes with allylboronates in aqueous media have been developed. In contrast to conventional allylboration reactions of aldehydes in organic solvents, the α‐addition products were obtained exclusively. A catalytic cycle in which the allylzinc species was generated through a B‐to‐Zn exchange process is proposed and kinetic studies were performed. The key intermediate, an allylzinc species, was detected by HRMS (ESI) analysis and by online continuous MS (ESI) analysis. This analysis revealed that, in aqueous media, the allylzinc species competitively reacted with the aldehydes and water. An investigation of the reactivity and selectivity of the allylzinc species by using several typical allylboronates ( 6a , 6b , 6c , 6d ) clarified several important roles of water in this allylation reaction. The allylation reactions of aldehydes with allylboronic acid 2,2‐dimethyl‐1,3‐propanediol esters proceeded smoothly in the presence of catalytic amounts of Zn(OH)₂ and achiral ligand 4d in aqueous media to afford the corresponding syn‐adducts in high yields with high diastereoselectivities. In all cases, the α‐addition products were obtained and a wide substrate scope was tolerated. Furthermore, this reaction was applied to asymmetric catalysis by using chiral ligand 9 . Based on the X‐ray structure of the Zn‐ 9 complex, several nonsymmetrical chiral ligands were also found to be effective. This reaction was further applied to catalytic asymmetric alkylallylation, chloroallylation, and alkoxyallylation processes and the synthetic utility of these reactions has been demonstrated.     

A Facile One‐pot Synthesis of α‐Halo,α‐allylic Aldehydes from α,α‐Dihalo Ketones Utilizing Allylic Zinc Bromide

An efficient synthesis of various α‐halo,α‐allylic aldehydes from α,α‐dihalo ketones using both cyclic (3‐bromocyclohex‐1‐ene zinc bromide and (Z)‐3‐bromocyclobut‐1‐ene zinc bromide) and acyclic (allylzinc bromide and cinnamylzinc bromide) type of allylic organozinc bromide with DMF as base is described. A possible reaction mechanism is also proposed.     

Mean enthalpy of disruption to valence state for homoleptic transition metal carbonyls. A reassessment

Under suitable conditions, the reaction of allylzinc bromide with a carbonyl compound can be reversible.     

Action of Organometallic Compounds on N-Cyanomethylimidate: New Synthetic Methode of Oxazole

The reaction of N-cyanomethylimidates with allylzinc bromide species has been examined. This reaction leads to the synthesis of oxazoles with good yields.     

Synthesis of (−)‐Erythrodiene and (+)‐7‐Epispirojatamol via Intramolecular Pd‐Catalyzed Allylzincation

Two spirobicyclic sesquiterpenoids, (−)‐erythrodiene ( 1 ) and (+)‐7‐epispirojatamol ( 30 ), were synthesized in enantiomerically pure form via an intramolecular allylzincation process. The allylzinc species were formed in the presence of Et₂Zn via transmetallation of a catalytically generated allylpalladium intermediate. Several Pd catalysts were tested for this transformation, and [Pd(OAc)₂]/Bu₃P (1 equiv.) was found to be, by far, the most effective. Whereas the preparation of 1 involved allylzincation of a tethered terminal olefin, 30 was formed via a novel intramolecular allyl zincation of a methyl ketone. Both reactions showed the same stereochemical preference, yielding the spirobicyclic products in 95 : 5 and 4 : 1 diastereoisomer ratios, respectively.     

A New Method for the Synthesis of Allyl Arylselenides via the Reaction of the Zinc Allyl Selenoates with Diaryliodonium Salts

The insertion of elemental selenium into the Zn-C bond of allylzinc bromide in THF leads to the corresponding zinc allyl selenoate. It reacts with diaryliodonium salts in THF-HMPA to afford the allyl arylselenides in high yields.     

Reaction of allylzinc reagents and zinc enolates of ketones with alpha-amidoalkylphenyl sulfones

Alpha-amidoalkylphenyl sulfones behave as N-acylimino equivalents in the reaction with functionalized allylzinc reagents. The addition products obtained using the zinc derivative of ethyl 2-(bromomethyl)acrylate can be readily transformed into alpha-methylene-gamma-lactams using different cyclization procedures. The allylzinc reagent obtained from 3-bromo-1-acetoxy-1-propene directly affords protected 1,2-amino alcohols with a preference for the anti stereoisomer, regardless of the structure of the alpha-amidoalkylphenyl sulfone employed. This procedure can be extended to the use of zinc enolates obtained from alpha-bromo ketones and leads to the synthesis of N-protected beta-amino ketones.     

Domino addition of allylzinc bromide to nitrile oxides: synthesis of 5-butenylisoxazolines

Nitrile oxides undergo addition to allylzinc bromide to generate 5-butenylisoxazolines in good yields.     

Dimerization of the allylzinc cation: selective coupling of allyl anions in a metallo-ene reaction

Metal assistance: Dimerization of the allylzinc monocation gives the dimetalated coupling product in quantitative yield. Kinetic and thermodynamic parameters of this reversible metallo-ene reaction have been determined. This reaction serves as a model system for the alkali-metal catalyzed production of 4-methylpentene.     

Enantioselective allylation of aldehydes promoted by chiral sulfur reagents

The addition of allylzinc bromide to aldehydes was studied with different chiral sulfur compounds acting as a catalyst. Yield differences and enantiomeric excesses were observed.     

Palladium-Catalyzed Carbonyl Allylation of Aldehydes with Allylic Phosphates: Synthesis of Homoallylic Alcohols

Allylation of aldehydes by reaction allylic phosphates with diethylzinc in the presence of Pd(PPh₃)₄ afforded homoallylic alcohol via nucleophilic allylzinc species.     

Solvent-Free Addition Reaction of Allylzinc Bromide and Aldimines

Barbier-type allylation of aldimines with allylzinc bromide took place rapidly under solvent-free conditions. The procedure is environmentally benign and operationally simple, has good regioselectivity, and gives good to excellent yields.     

Diastereoselective Addition of Organozinc Reagents to Benzaldiminetricarbonylchromium Derivatives

Abstract

The reaction of benzaldiminetricarbonylchromium derivatives with benzylzinc bromide or allylzinc bromide in the presence of BF₃ · Et₂ O gave the corresponding amine complexes with high diastereoselectivities.     

Synthese de β-ethoxycarbonyl λ-lactones

β-ethoxycarbonyl β, λ-insaturated λ-lactones 2 are easily prepared by dehydration of β-acyl β-ethoxycarbonyl α-alkyl propionic acids. Otherwise the condensation of these acids with allylzinc reagents produces β-ethoxycarbonyl λ-lactones 3 with a β-ethylenic carbon chain branched on the λ-carbon of the lactone.     

Solvent- and catalyst-free gem-bisallylation of carboxylic acid derivatives with allylzinc bromide

A rapid and efficient procedure for the solvent-free synthesis of gem-bisallylation products has been achieved by allylzinc bromide with carboxylic acid derivatives in the absence of any catalysts at room temperature.     

Direct carbohydrate to carbocycle conversions via intramolecular allylation with Et2Zn/Pd(0)

Treatment of 5-vinylpyranosides with Et₂Zn and catalytic Pd(0), in the presence of ZnCl₂, results in the formation of 5-membered carbocyclic products. This carbohydrate ring-contraction features an intramolecular allylation of a ring-opened carbohydrate aldehyde by an in situ-generated nucleophilic allylzinc species. The stereoselectivity about vinyl and free hydroxyl groups at the newly created stereogenic centers varies from low to moderate while both its extent and sense are found to depend on particular structural features (e.g. the configuration of the starting carbohydrate).     

A novel entry to C-glycals via diethylzinc-mediated umpolung of π-allyl palladium derived from 1-exo-methylene 2,3-anhydrofuranoses

The reaction of aldehydes with allylzinc reagents resulting from the umpolung of π-allyl palladium complexes from 1-exo-methylene 2,3-anhydrofuranoses provides a novel entry to C-glycals.     

A convenient approach to total synthesis of synargentolide-B from l-ascorbic acid and d-ribose

A convenient and practical approach for the total synthesis of naturally occurring lactone synargentolide-B has been accomplished in 14 steps from the commercially available l-ascorbic acid and d-ribose involving Bestmann–Ohira reaction, zinc mediated allylation, ring closing-metathesis, and cross-metathesis reactions. The highlight of our strategy describes a one-pot reaction involving stereoselective addition of allylzinc reagent and selective reduction of terminal alkyne to obtain the key advanced intermediates.     

Cobalt- and rhodium-catalyzed cross-coupling reaction of allylic ethers and halides with organometallic reagents

Reactions of 2-alkenyl methyl ether with phenyl, trimethylsilylmethyl, and allyl Grignard reagents in the presence of cobalt(II) complexes are discussed. The success of the reactions heavily depends on the combination of the substrate, ligand, and Grignard reagent. In the reaction of cinnamyl methyl ether, the formation of the linear coupling products predominates over that of the relevant branched products. In the cobalt-catalyzed allylation of allylic ethers, addition of a diphosphine ligand can change the regioselectivity, mainly providing the corresponding branched products. Rhodium complexes catalyze the reactions of allylic ethers and halides with allylmagnesium chloride and allylzinc bromide, respectively, in which the branched coupling product is the major product.     

Reactivity of chiral alpha-amidoalkylphenyl sulfones with stabilized carbanions. stereoselective synthesis of optically active 1-aminopyrrolizidine

Metal enolates and functionalized allylzinc reagents react with optically active alpha-amidoalkylphenyl sulfones to give N-carbamoylamino derivatives with variable levels of anti diastereoselectivity. Zinc enolates provide comparable results with respect to lithium enolates in terms of diastereoselectivity but afford beta-amino ester derivatives in lower yield. The synthetic utility of the obtained chiral N-carbamoylamino esters is demonstrated by the first enantioselective synthesis of (-)-1-aminopyrrolizidine a central intermediate for the preparation of various biologically active substances.