Allylic Electrophiles Research Articles

Copper-Catalyzed SN2′-Selective Allylic Substitution Reaction of gem-Diborylalkanes

A Cu/(NHC)-catalyzed SN2'-selective substitution reaction of allylic electrophiles with gem-diborylalkanes is reported. Different substituted gem-diborylalkanes and allylic electrophiles can be employed in this reaction, and various synthetic valuable functional groups can be tolerated. The asymmetric version of this reaction was initially researched with chiral N-heterocyclic carbene (NHC) ligands.

ChemInform Abstract: Iridium‐Catalyzed Enantioselective Fluorination of Racemic, Secondary Allylic Trichloroacetimidates.

The Ir-catalyzed enantioselective fluorination of racemic, branched allylic trichloroacetimidates with Et3N·3HF is a mild and efficient route for selective incorporation of fluoride ion into allylic systems. We herein describe the asymmetric fluorination of racemic, secondary allylic electrophiles with Et3N·3HF using a chiral-diene-ligated Ir complex. The methodology enables the formation of acyclic fluorine-containing compounds in good yields with excellent levels of asymmetric induction and overcomes the limitations previously associated with the enantioselective construction of secondary allylic fluorides bearing α-linear substituents.

Regioselective Allylation of Carbon Electrophiles with Alkenyl­silanes under Dual Catalysis by Cationic Platinum(II) Species

In the presence of catalytic amounts of platinum(II) chloride and silver(I) hexafluoroantimonate, (Z)-alkenylsilanes reacted with various carbon electrophiles (acetals, aminals, carboxylic anhydrides, alkyl chlorides, etc.) at the γ-position to give allylation products. A plausible mechanism for the platinum-catalyzed allylation involves alkene migration of alkenylsilanes to allylsilanes and subsequent allylation of carbon electrophiles, both of which are catalyzed by a cationic platinum(II) species.

Iridium-Catalyzed Enantioselective Fluorination of Racemic, Secondary Allylic Trichloroacetimidates.

The Ir-catalyzed enantioselective fluorination of racemic, branched allylic trichloroacetimidates with Et3N·3HF is a mild and efficient route for selective incorporation of fluoride ion into allylic systems. We herein describe the asymmetric fluorination of racemic, secondary allylic electrophiles with Et3N·3HF using a chiral-diene-ligated Ir complex. The methodology enables the formation of acyclic fluorine-containing compounds in good yields with excellent levels of asymmetric induction and overcomes the limitations previously associated with the enantioselective construction of secondary allylic fluorides bearing α-linear substituents.

FeCl3 catalysed regioselective allylation of phenolic substrates with (α-hydroxy)allylphosphonates

Electrophilic allylation of phenolic substrates including salicylaldehydes with (α-hydroxy) allylphosphonates is presented. It is observed that catalytic FeCl3 is sufficient to accomplish the allylation. Interestingly, the reaction led to the formation of allylphosphonates in addition to vinylphosphonates, depending upon the substituent. The vinylphosphonates obtained here are E-isomers. More importantly, the reaction occurred regioselectively with respect to the phenolic substrates. Substituted allylphosphonates are formed when salicylaldehyde or (2-hydroxy-phenyl)arylmethanones are used. Conclusive proof for the formation of allylphosphontates as well as vinylphosphonates has been provided by single crystal X-ray crystallography. Regioselective allylation of phenolic substrates using phosphono-allyl alcohols was achieved by using even catalytic amounts of FeCl3. Both vinylphosphonates and allylphosphonates are obtained, the ratio depending upon the substrate.

ChemInform Abstract: Catalyst‐Directed Diastereo‐ and Site‐Selectivity in Successive Nucleophilic and Electrophilic Allylations of Chiral 1,3‐Diols: Protecting‐Group‐Free Synthesis of Substituted Pyrans.

AbstractA straightforward strategy for the synthesis of different diastereomers of 4‐hydroxy‐2,6‐disubstituted pyrans is described.

A Catalytic Asymmetric Total Synthesis of (-)-Perophoramidine.

We report a catalytic asymmetric total synthesis of the ascidian natural product perophoramidine. The synthesis employs a molybdenum-catalyzed asymmetric allylic alkylation of an oxindole nucleophile and a monosubstituted allylic electrophile as a key asymmetric step. The enantioenriched oxindole product from this transformation contains vicinal quaternary and tertiary stereocenters, and is obtained in high yield along with high levels of regio-, diastereo-, and enantioselectivity. To install the second quaternary stereocenter in the target, the route utilizes a novel regio- and diastereoselective allylation of a cyclic imino ether to deliver an allylated imino ether product in near quantitative yield and with complete regio- and diastereocontrol. Oxidative cleavage and reductive amination are used as final steps to access the natural product.

Platinum-catalyzed allylation of carbon electrophiles with alkenylsilanes

In the presence of catalytic amounts of PtCl2 and AgSbF6, (Z)-alkenylsilanes react with various carbon electrophiles at the γ-position to give allylation products. A plausible mechanism for the Pt-catalyzed allylation involves alkene migration of alkenylsilanes to allylsilanes and subsequent allylation of carbon electrophiles.

ChemInform Abstract: Iron‐Catalyzed Cross‐Coupling Reactions

AbstractReview: 190 refs.

ChemInform Abstract: Congested C—C Bonds by Pd‐Catalyzed Enantioselective Allyl—Allyl Cross‐Coupling, a Mechanism‐Guided Solution.

Under the influence of a chiral bidentate diphosphine ligand, the Pd-catalyzed asymmetric cross-coupling of allylboron reagents and allylic electrophiles establishes 1,5-dienes with adjacent stereocenters in high regio- and stereoselectivity. A mechanistic study of the coupling utilizing reaction calorimetry and density functional theory analysis suggests that the reaction operates through an inner-sphere 3,3′-reductive elimination pathway, which is both rate-defining and stereodefining. Coupled with optimized reaction conditions, this mechanistic detail is used to expand the scope of allyl–allyl couplings to allow the generation of 1,5-dienes with tertiary centers adjacent to quaternary centers as well as a unique set of cyclic structures.

ChemInform Abstract: N‐Heterocyclic Carbene Catalyzed Intramolecular Acylation of Allylic Electrophiles.

AbstractThe first N‐heterocyclic carbene‐catalyzed intramolecular SN2′ substitution reaction of an aldehyde with allylic electrophiles, followed by isomerization to give α,β‐unsaturated chromanones and related compounds is developed.

First evidence for the use of polyamines as nucleophiles in a regioselective palladium-catalyzed allylic amination reaction

Palladium-catalyzed reaction of unsymmetrical allylic electrophiles with polyamines gives rise to regioisomeric allylic polyamines. An original catalytic procedure providing an efficient method for the regioselective synthesis of new classes of polyamino derivatives of biological interest is reported. Based on experimental considerations, a mechanistic rationale involving a thermodynamically controlled isomerization of the initially formed branched product is proposed to account for the total regioselectivity observed.

Multicomponent decarboxylative allylations.

The reaction of Meldrum's acid, pyrrolide, and allyl carbonates allows a multicomponent decarboxylative coupling to form allylated acyl pyrroles. This strategy is made possible by the in situ formation of β-oxo carboxylates from Meldrum's acid. Subsequent decarboxylative enolate formation and electrophilic allylation complete the reaction. Addition of benzylidene malononitriles as good Michael acceptors allow a 4-component interceptive decarboxylative allylation.

Reactions of organozinc reagents with potassium bromodifluoroacetate

Assembling of gem -difluorinated compounds from organozinc reagents, potassium bromodifluoroacetate and electrophiles is described. • Synthesis of gem -difluorinated compounds. • Preparation and reactions of fluorinated organozinc reagents. • Reactions of potassium boromodifluoroacetate. A practical method for the synthesis of gem -difluorinated compounds from organozinc reagents is described. Potassium bromodifluoroacetate serves as a source of CF 2 -fragment, which is inserted into carbon zinc bond of organozinc reagents. The intermediate difluorinated organozinc species can be protonated, brominated or coupled with allylic electrophiles.

Catalyst-directed diastereo- and site-selectivity in successive nucleophilic and electrophilic allylations of chiral 1,3-diols: protecting-group-free synthesis of substituted pyrans.

The iridium-catalyzed, protecting group-free synthesis of 4-hydroxy-2,6-cis- or trans-pyrans through successive nucleophilic and electrophilic allylations of chiral 1,3-diols occurs with complete levels of catalyst-directed diastereoselectivity in the absence of protecting groups, premetallated reagents, or discrete alcohol-to-aldehyde redox reactions.

Reactivity of mixed organozinc and mixed organocopper reagents: 11. Nickel‐catalyzed atom‐economic aryl–allyl coupling of mixed (n‐alkyl)(aryl)zincs

Group selectivity in the allylation of mixed (n‐butyl)(phenyl)zinc reagent can be controlled by changing reaction parameters. CuCN‐catalyzed allylation in tetrahydrofuran (THF)–hexamethylphosphoric triamide is n‐butyl selective and also γ‐selective in the presence of MgCl2, whereas CuI‐catalyzed allylation in THF in the presence of n‐Bu3P takes place with a n‐butyl transfer:phenyl transfer ratio of 23:77 and an α:γ transfer ratio of phenyl of 76:24. NiCl2(Ph3P)2‐catalyzed allylation in the presence of LiCl is phenyl selective with an α:γ ratio of 65:35. The reaction of methyl‐ or n‐butyl(aryl)zinc reagents with an allylic electrophile in THF at room temperature in the presence of NiCl2(Ph3P)2 catalyst and LiCl as an additive provides an atom‐economic alternative to aryl–allyl coupling using diarylzincs. Copyright © 2014 John Wiley & Sons, Ltd.

ChemInform Abstract: Copper‐Catalyzed Allylation of α,α‐Difluoro‐Substituted Organozinc Reagents.

A method for the coupling of organozinc reagents, difluorocarbene, and allylic electrophiles is described. The reaction involves insertion of difluorocarbene into the carbon–zinc bond followed by copper-catalyzed allylic substitution.

Asymmetric palladium-catalyzed allylic alkylation using dialkylzinc reagents: a remarkable ligand effect.

A serendipitously discovered palladium-catalyzed asymmetric allylic alkylation reaction with diorganozinc reagents, which displays broad functional group compatibility, is reported. This novel transformation hinges on a remarkable ligand effect which overrides the standard "umpolung" reactivity of allyl-palladium intermediates in the presence of dialkylzincs. Owing to its mild conditions, enantioselective allylic alkylations of racemic allylic electrophiles are possible in the presence of sensitive functional groups.

N-heterocyclic carbene catalyzed intramolecular acylation of allylic electrophiles.

The N-heterocyclic carbene (NHC) catalyzed addition reaction has been well documented recently; however, the NHC-catalyzed substitution reaction especially the SN2' type reaction remains a challenge. As one of the most fundamental reaction types in organic chemistry, the SN2' reaction catalyzed by NHC would be a powerful tool in organic synthesis. Therefore, the first NHC-catalyzed intramolecular SN2' substitution reaction of aldehyde with allylic electrophiles has been developed. A variety of α,β-unsaturated chromanones were obtained under a domino SN2' reaction and isomerization. Mechanistic experiments were conducted to confirm the nature of this SN2' reaction.

Congested C-C bonds by Pd-catalyzed enantioselective allyl-allyl cross-coupling, a mechanism-guided solution.

Under the influence of a chiral bidentate diphosphine ligand, the Pd-catalyzed asymmetric cross-coupling of allylboron reagents and allylic electrophiles establishes 1,5-dienes with adjacent stereocenters in high regio- and stereoselectivity. A mechanistic study of the coupling utilizing reaction calorimetry and density functional theory analysis suggests that the reaction operates through an inner-sphere 3,3'-reductive elimination pathway, which is both rate-defining and stereodefining. Coupled with optimized reaction conditions, this mechanistic detail is used to expand the scope of allyl-allyl couplings to allow the generation of 1,5-dienes with tertiary centers adjacent to quaternary centers as well as a unique set of cyclic structures.