Homoallylic Amines Research Articles

Redox-Neutral 1,4-Dicarbonfunctionalization of 1,3-Butadiene by Merging Photoredox and Nickel Catalysis.

The diverse functionalization of 1,3-butadiene provides wide applicability toward the synthesis of abundant and useful allylic compounds. Here, we describe a three-component and redox-neutral assembly of readily available C═X compounds, 1,3-butadiene, and various nucleophiles by merging photoredox and nickel catalysis, enabling the rapid synthesis of structurally diverse homoallyl amines and homoallylic alcohols.

Brookhart's Acid-Catalyzed Switchable Regioselective N-Alkylation of Arylamines/Heterocyclic Amines with Cyclopropylcarbinols by Temperature Regulation.

An unprecedented, Brookhart's acid-catalyzed temperature-switchable regioselective divergent approach for N-alkylation of arylamines and heterocyclic amines by utilising cyclopropylcarbinols is presented herein. The reaction offers N-alkylated cyclopropyl derivatives and homoallyl amines by employing 2.5 mol% catalyst loading at different temperatures in excellent regioselectivity and yields. This method has shown to be relevant with a wide range of cyclopropylcarbinols, including aliphatic ones. Several control experiments and spectroscopic studies have been performed to gain insight into the reaction mechanism. Further, the synthetic utility of the protocol has also been described.

γ C-H Functionalization of Amines via Triple H-Atom Transfer of a Vinyl Sulfonyl Radical Chaperone.

A selective, remote desaturation has been developed to rapidly access homoallyl amines from their aliphatic precursors. The strategy employs a triple H-atom transfer (HAT) cascade, entailing (i) cobalt-catalyzed metal-HAT (MHAT), (ii) carbon-to-carbon 1,6-HAT, and (iii) Co-H regeneration via MHAT. A new class of sulfonyl radical chaperone (to rapidly access and direct remote, radical reactivity) enables remote desaturation of diverse amines, amino acids, and peptides with excellent site-, chemo-, and regioselectivity. The key, enabling C-to-C HAT step in this cascade was computationally designed to satisfy both thermodynamic (bond strength) and kinetic (polarity) requirements, and it has been probed via regioselectivity, isomerization, and competition experiments. We have also interrupted this radical transfer dehydrogenation to achieve γ-selective C-Cl, C-CN, and C-N bond formations.

Rhodium-/Iridium-Catalyzed Hydroamination for the Synthesis of 1,2-, 1,3-, or 1,4-Diamines.

An Ir-catalyzed regioselective hydroamination of allyl amines using aryl amines and catalyst-controlled regiodivergent hydroamination of allylic and homoallylic amines with aniline nucleophiles are reported. The directed hydroamination reactions afford a variety of 1,2-, 1,3-, and 1,4-diamines in good to excellent yields and high regio- and chemoselectivities. Mechanistic investigations suggests that the reactions are proceeding through an oxidative addition into the ArHN-H bond and that the observed regioselectivity is due to the selective formation of a 5- or 6-membered metalacyclic intermediate, depending on the catalyst employed.

CuH-Catalyzed Enantioselective Reductive Coupling of 1,3-Dienes and Trifluoromethyl Ketoimines or α-Iminoacetates.

The intermolecular addition of allylic copper species generated from diene and copper hydride remains elusive. Herein copper hydride catalyzed asymmetric cross reductive coupling of conjugated dienes and ketoimines including trifluoromethyl ketoimines and α-iminoacetates was first achieved using chiral Ph-BPE as the ligand, providing rapid access to structurally and optically enriched homoallylic amines containing two vicinal stereogenic centers with up to 95% yield, 99% ee, and 11:1 diastereoselectivities.

Synthesis of Homoallylic Amines by Radical Allylation of Imines with Butadiene under Photoredox Catalysis

AbstractIonic (2 e−) nucleophilic addition of allylmetal regents to imines dominates the synthesis of homo‐allyl amine; however, single electron (1 e−) mediated imine allylation with feedstocks butadiene as an alternative allyl source remains unexplored. In this work, we report a conceptually different radical–radical cross‐coupling strategy for the synthesis of a homoallyl amine between an α‐amino alkyl radical and a transient allylic radical. This metal‐free method provided a novel approach for the synthesis of homoallylic amines (>80 examples) from readily available materials with excellent regioselectivity and exceptional broad functional group compatibility.

Synthesis of Homoallylic Amines by Radical Allylation of Imines with Butadiene under Photoredox Catalysis.

Ionic (2 e- ) nucleophilic addition of allylmetal regents to imines dominates the synthesis of homo-allyl amine; however, single electron (1 e- ) mediated imine allylation with feedstocks butadiene as an alternative allyl source remains unexplored. In this work, we report a conceptually different radical-radical cross-coupling strategy for the synthesis of a homoallyl amine between an α-amino alkyl radical and a transient allylic radical. This metal-free method provided a novel approach for the synthesis of homoallylic amines (>80 examples) from readily available materials with excellent regioselectivity and exceptional broad functional group compatibility.

Efficient access to general α-tertiary amines via water-accelerated organocatalytic multicomponent allylation

A tetrasubstituted carbon atom connected by three sp3 or sp2-carbons with single nitrogen, i.e., the α-tertiary amine (ATA) functional group, is an essential structure of diverse naturally occurring alkaloids and pharmaceuticals. The synthetic approach toward ATA structures is intricate, therefore, a straightforward catalytic method has remained a substantial challenge. Here we show an efficient water-accelerated organocatalytic method to directly access ATA incorporating homoallylic amine structures by exploiting readily accessible general ketones as useful starting material. The synergistic action of a hydrophobic Brønsted acid in combination with a squaramide hydrogen-bonding donor under aqueous condition enabled the facile formation of the desired moiety. The developed exceptionally mild but powerful system facilitated a broad substrate scope, and enabled efficient multi-gram scalability.

19F magnetic resonance probes for detecting formaldehyde

Herein we report two separate 19F magnetic resonance (MR) probes responsive towards formaldehyde. Both agents were synthesized in a single step via aminoallylation of either 4-fluorobenzaldehyde (1FA) or 4-(trifluoromethyl)benzaldehyde (3FA) with ammonia and allylboronic acid pinacol ester. Condensation of the resulting homoallylic amines 1FA and 3FA with formaldehyde, followed by a 2-aza-Cope rearrangement and subsequent hydrolysis affords 4-fluorobenzaldehyde and 4-(trifluoromethyl)benzaldehyde, respectively. In the case of 1FA, this transformation is evidenced by a concomitant downfield shift in the 19F MR signal from −115 ppm to −103 ppm. Further, this transformation is selective towards formaldehyde over other reactive carbonyl species. While 3FA exhibits similar selectivity towards formaldehyde, this more sensitive probe is limited by the small chemical shift difference (0.7 ppm) following its activation.

1,3-Asymmetric Induction in Diastereoselective Allylations of Chiral N-Tosyl Imines.

Lewis acid mediated allylations of β-alkoxy N-tosyl imines using allyltrimethylsilane lead to 3-alkoxy homoallylic N-tosyl amines with anti-selectivity. Two methods of Cu(OTf)2-mediated allylations are reported herein, demonstrating that diastereoselectivity can be achieved through 1,3 acyclic stereocontrol of β-chiral aldimines. Observed selectivity trends and computational evidence suggest selectivity arises through the formation of a six-membered ring chelate. The product ratios of these allylations are dependent on conformational preferences of the chelate and steric effects in the transition-state structures.

Regioselective nickel-catalyzed dicarbofunctionalization of unactivated alkenes enabled by picolinamide auxiliary

Catalytic difunctionalization of alkenes has been a prominent research theme in recent years. Here, we develop a removable bidentate picolinamide-assisted regioselective dicarbofunctionalization of homoallylic amines with organohalides and arylboronic acids. The catalytic system, using cost-effective and air-stable Ni(II) precatalyst, which could be activated by arylboronic acids, provides access to the regioselective diarylation and arylalkylation of unactivated alkenes. This reaction is compatible with α- or β-substituted terminal alkenes and internal alkenes and exhibits excellent functional group and heterocycle tolerance. Preliminary mechanistic studies suggest that the reaction proceeds via a NiI/NiIII catalytic cycle rather than a Ni0/NiII cycle. Notably, the general and practical protocol developed herein represents, to the best of our knowledge, the first example of Ni-catalyzed 3-component 2,1-diarylation and arylalkylation of alkenes with arylboronic acids and organohalides.

Exploiting Iminoquinones as Electrophilic at Nitrogen "N+" Synthons for C-N Bond Construction.

New methods for C-N bond construction exploiting the N-centered electrophilic character of iminoquinones are reported. Iminoquinones, generated in situ via the condensation of o-vinylanilines with benzoquinones, undergo acid-catalyzed cyclization to afford N-arylindoles in excellent yields. Under similar reaction conditions, homoallylic amines react analogously to afford N-arylpyrroles. Additionally, organometallic nucleophiles are shown to add to the nitrogen atom of N-alkyliminoquinones to provide amine products. Finally, iminoquinones are shown to be competent electrophiles for copper-catalyzed hydroamination.

Visible-light photoredox-promoted desilylative allylation of α-silylamines: An efficient route to synthesis of homoallylic amines

A facile and efficient synthesis of homoallylic amines by visible-light photoredox-promoted desilylative allylation of α-silylamines with allylic sulfones is described. A variety of α-silylamines derived from anilines, cyclic and acyclic alkyl amines reacted with a serious of mono or disubstituted allylic sulfones well to provide homollylic amines in good to high yields under very mild reaction conditions.

Stereoselective Synthesis of C‐Vinyl Glycosides via Palladium‐Catalyzed C−H Glycosylation of Alkenes

AbstractC‐vinyl glycosides are an important class of carbohydrates and pose a unique synthetic challenge. A new strategy has been developed for stereoselective synthesis of C‐vinyl glycosides via Pd‐catalyzed directed C−H glycosylation of alkenes with glycosyl chloride donors using an easily removable bidentate auxiliary. Both the γ C−H bond of allylamines and the δ C−H bond of homoallyl amine substrates can be glycosylated in high efficiency and with excellent regio‐ and stereoselectivity. The resulting C‐vinyl glycosides can be further converted to a variety of C‐alkyl glycosides with high stereospecificity. These reactions offer a broadly applicable method to streamline the synthesis of complex C‐vinyl glycosides from easily accessible starting materials.

Stereoselective Synthesis of C-Vinyl Glycosides via Palladium-Catalyzed C-H Glycosylation of Alkenes.

C-vinyl glycosides are an important class of carbohydrates and pose a unique synthetic challenge. A new strategy has been developed for stereoselective synthesis of C-vinyl glycosides via Pd-catalyzed directed C-H glycosylation of alkenes with glycosyl chloride donors using an easily removable bidentate auxiliary. Both the γ C-H bond of allylamines and the δ C-H bond of homoallyl amine substrates can be glycosylated in high efficiency and with excellent regio- and stereoselectivity. The resulting C-vinyl glycosides can be further converted to a variety of C-alkyl glycosides with high stereospecificity. These reactions offer a broadly applicable method to streamline the synthesis of complex C-vinyl glycosides from easily accessible starting materials.

Transition-metal-free allylation of 2-azaallyls with allyl ethers through polar and radical mechanisms

Allylation of nucleophiles with highly reactive electrophiles like allyl halides can be conducted without metal catalysts. Less reactive electrophiles, such as allyl esters and carbonates, usually require a transition metal catalyst to facilitate the allylation. Herein, we report a unique transition-metal-free allylation strategy with allyl ether electrophiles. Reaction of a host of allyl ethers with 2-azaallyl anions delivers valuable homoallylic amine derivatives (up to 92%), which are significant in the pharmaceutical industry. Interestingly, no deprotonative isomerization or cyclization of the products were observed. The potential synthetic utility and ease of operation is demonstrated by a gram scale telescoped preparation of a homoallylic amine. In addition, mechanistic studies provide insight into these C(sp3)–C(sp3) bond-forming reactions.

Ni-Catalyzed Reductive Allylation of α-Chloroboronates to Access Homoallylic Boronates.

The transition-metal-catalyzed allylation reaction is an efficient strategy for the construction of new carbon-carbon bonds alongside allyl or homoallylic functionalization. Herein we describe a Ni-catalyzed reductive allylation of α-chloroboronates to efficiently render the corresponding homoallylic boronates, which could be readily converted into valuable homoallylic alcohols or amines or 1,4-diboronates. This reaction features a broad substrate scope with good functional group compatibility that is complementary to the existing methods for the preparation of homoallylic boronates.

Enantioselective, Catalytic Multicomponent Synthesis of Homoallylic Amines Enabled by Hydrogen-Bonding and Dispersive Interactions.

We report a one-step catalytic, enantioselective method for the preparation of homoallylic N-Boc amines directly from acetals. Reactive iminium ion intermediates are generated in situ through the combination of an acetal, a chiral thiourea catalyst, trialkylsilyl triflate, and N-Boc carbamate and are subsequently trapped by a variety of allylsilane nucleophiles. No homoallylic ether byproducts are detected, consistent with allylation of the iminium intermediate being highly favored over allylation of the intermediate oxocarbenium ion. Acetals derived from aromatic aldehydes possessing a variety of functional groups and substitution patterns yield homoallylic amines with excellent levels of enantiomeric enrichment. Experimental and computational data are consistent with an anchoring hydrogen-bond interaction between the protioiminium ion and the amide of the catalyst in the enantiodetermining transition state, and with stereodifferentiation achieved through specific noncovalent interactions (NCIs) with the catalyst pyrenyl moiety. Evidence is provided that the key NCI in the major pathway is a π-stacking interaction, contrasting with the cation-π interactions invoked in previously studied reactions promoted by the same family of aryl-pyrrolidino-H-bond-donor catalysts.

Making and breaking of Zn–C bonds in the cases of allyl and propargyl organozincs

This review aims to sum up recent developments in the synthesis of homoallylic and homopropargylic alcohols or amines by using methods based on catalytic or stoichiometric use of metallic zinc for allylation and propargylations of carbonyls or imines. These methods encompass various transformations which are now commonly expressed as Barbier-Grignard type reactions including several chemical or electrochemical processes.

Ni-Catalyzed Coupling of Butadiene, Aldimines, and Arylboronic Acids to Homoallylic Amines under Base-Free Conditions

Herein, we report a nickel-catalyzed three-component coupling of butadiene, aldimines, and arylboronic acids to form synthetically important homoallylic amines. The starting materials are stable an...