Homoallylic Amines Research Articles

Cobalt-Catalyzed Carbonylative Cyclization of Homoallylic Alcohols and Amines

Cobalt-Catalyzed Carbonylative Cyclization of Homoallylic Alcohols and Amines

Asymmetric organocatalytic synthesis of chiral homoallylic amines.

In recent decades, the chiral allylation of imines emerged as a key methodology in the synthesis of alkaloids and natural products with 4-, 5- and 6-membered cyclic amine motifs. Initially reliant on stoichiometric reagents, synthetic chemists predominantly used N-substituted chiral imines, organometallic chiral reagents and achiral reagents with an equimolar chiral controller. However, recent years have witnessed the rise of asymmetric transition-metal catalysts and, importantly, organocatalytic allylation, reshaping the landscape of modern synthetic chemistry. This review explores the latest developments in the asymmetric allylation of imines, encompassing cutting-edge advances in hydrogen-bond catalysis and non-classical approaches. Furthermore, practical examples showcasing the application of these innovative methodologies in total synthesis are presented.

Lewis Acid‐Promoted Domino Processes for the Synthesis of Homoallylic Amines, Quinolines and Tetrahydroquinolines

AbstractHerein, the synthesis of homoallylic amines, quinolines, and tetrahydroquinolines has been demonstrated. The domino one‐pot multi‐component approach has been accomplished using Lewis acid‐catalyzed conditions. A useful scaffold construction strategy can be achieved by controlling the electronic effect of aniline rather than relying on reaction conditions. The described method applies to a wide variety of substrates embedded with diverse functional groups and can be extended toward the synthesis of natural products. Suitable control experiments, real‐time NMR studies, and DFT calculations have validated the reported process. The protocol outlines a strategy for synthesizing homoallylic amines and quinolines, controlled by the electronic properties of anilines.

Copper-Catalyzed Three-Component 1,5-Carboamination of Vinylcyclopropanes.

The 1,5-copper-catalyzed carboamination of vinylcyclopropanes is presented. A carbon-centered radical, formed upon reduction of an alkyl halide by Cu(I), adds across the alkene of a vinylcyclopropane, triggering ring opening to generate a benzylic radical, which, finally, undergoes copper-mediated amination to afford a homoallylic amine. The reaction occurs with outstanding regio- and good to very good diastereoselectivities. The scope of the reaction is demonstrated with respect to all three components: alkyl halide, vinylcyclopropane, and amine nucleophile. A total of 38 examples are presented with an average yield of 60%.

Organic Dye Photocatalyzed Synthesis of Functionalized Lactones and Lactams via a Cyclization-Alkynylation Cascade.

An organic dye photocatalyzed lactonization-alkynylation of easily accessible homoallylic cesium oxalates using ethynylbenziodoxolone (EBX) reagents has been developed. The reaction gave access to valuable functionalized lactones and lactams in up to 88% yield via the formation of two new C-C bonds. The transformation was carried out on primary, secondary, and tertiary homoallylic alcohols and primary homoallylic amines and could be applied to the synthesis of spirocyclic compounds as well as fused and bridged bicyclic lactones.

Asymmetric Allylation of Aldoxime Derivatives with β‐Amidoallylboronate in Water and Its Application to Divergent Synthesis of N‐Hydroxy‐γ‐Lactam and 1,2‐Oxazinan‐6‐one

AbstractA new application involving a water–stable amido–functionalized allylboronate has been developed for 1,2‐addition to carbon–nitrogen double bonds. The process achieves highly enantioselective allylation of aldoxime derivatives in water, by employing O‐Boc oximes as substrates under Zn(OH)2–chiral aminophenol catalysis. This process affords the corresponding homoallylic amines with 91–96 % ee. The products could be transformed into N‐hydroxy‐γ‐lactam or 1,2‐oxazinan‐6‐one, through an acidic or a protection‐acidic treatment sequence, respectively, almost without enantiopurity loss.

N-Triflyl Phosphoric Triamide (N-TPT) as an Efficient Activator for ‘On-Water’ Accelerated Aquacatalytic Polar Substrate Allylation

AbstractThe development of sustainable, functional-group-tolerant catalysis is highly significant from the perspectives of safety, user-friendliness, and cost-effectiveness. We report herein the triple hydrogen-bonding donor activator N-triflyl phosphoric triamide ( N-TPT) for the synergistic Brønsted acid aquacatalysis of multicomponent allylation ‘on-water’. The reaction demonstrated remarkable efficiency in converting polar diol substrate, such as 1,3-dihydroxyacetone, into α-tertiary amine derivative incorporating homoallylic amine functionalities using bulk water as the reaction medium. The single crystal X-ray structure and control experiments highlighted the crucial role of multiple hydrogen bonds in enabling this aqueous reaction.

Copper-Catalyzed Enantioselective 1,2-Allylation of Azadienes with Allylboronates.

Catalytic asymmetric 1,2-allylation of aurone-derived azadienes is very difficult to achieve due to the driving force for aromatization and the greater steric hindrance of 1,2-addition compared with 1,4-addition. By taking advantage of the ability of nitrogen ligated metal complexes, we successfully demonstrated the first example of copper-catalyzed 1,2-allylation of azadienes with allylboronates for the highly enantioselective synthesis of homoallylic amines. Meanwhile, the enantioenriched 1,4-addition products could also be obtained through a subsequent 3,3-sigmatropic rearrangement of the 1,2-addition products. Extensive DFT calculations were carried out to elucidate the origins of high regioselectivity (1,2- vs 1,4-) and enantioselectivity.

Asymmetric α-C(sp3)−H allylic alkylation of primary alkylamines by synergistic Ir/ketone catalysis

Primary alkyl amines are highly reactive in N-nucleophilic reactions with electrophiles. However, their α-C−H bonds are unreactive towards electrophiles due to their extremely low acidity (pKa ~57). Nonetheless, 1,8-diazafluoren-9-one (DFO) can activate primary alkyl amines by increasing the acidity of the α-amino C−H bonds by up to 1044 times. This makes the α-amino C−H bonds acidic enough to be deprotonated under mild conditions. By combining DFO with an iridium catalyst, direct asymmetric α-C−H alkylation of NH2-unprotected primary alkyl amines with allylic carbonates has been achieved. This reaction produces a wide range of chiral homoallylic amines with high enantiopurities. The approach has successfully switched the reactivity between primary alkyl amines and allylic carbonates from intrinsic allylic amination to the α-C−H alkylation, enabling the construction of pharmaceutically significant chiral homoallylic amines from readily available primary alkyl amines in a single step.

Cu-Catalyzed Direct Enantioselective Vinylogous Mannich Reaction between β,γ-Unsaturated Pyrazoleamides and Ketimines.

A catalytic asymmetric vinylogous Mannich-type reaction between β,γ-unsaturated amides and ketimines has been developed in excellent regio-, diastereo-, and enantioselectivities. The methodology provides an efficient approach to construct chiral homoallylic amines with a 3-amino-2-oxindole scaffold. Moreover, the transformations of the chiral products, including the removal of the pyrazole group or Boc group, the reduction of the C-C double bond, and Suzuki coupling, have been investigated.

Understanding mechanism driven regioselectivity in zirconium-catalysed hydroaminoalkylation: homoallylic amines from conjugated dienes.

The unexpected 4,1-hydroaminoalkylation of dienes provides selective access to linear homoallylic amines by zirconium catalysis. This switch from the traditional branched preferred regioselectivity to selective linear product formation using this early transition metal can be attributed to π-allyl intermediates. The reactivity of these isolated intermediates on a sterically accessible and coordinatively flexible chelating bis(ureate) Zr(iv) complex confirmed reversible C-C bond formation in hydroaminoalkylation catalysis.

Rh2(esp)2-catalyzed three-component reaction of a diazo compound, alkyl azide and allylboronate for the synthesis of homoallylic amine derivatives

The three-component reaction of the diazo compound, azide and allylboronate for preparation of homoallylic amine derivatives was explored, and Rh2(esp)2 was utilized as the optimal catalyst.

Iridium-catalysed hydroamination of internal homoallylic amines.

An Ir-catalysed regioselective hydroamination of internal homoallylic amines is reported. Both cyclic and acyclic internal olefins undergo directed hydroamination reactions with both aromatic and cyclic aliphatic amines to afford a variety of 1,4-diamines in fair to excellent yields. Diastereoselectivity and mechanistic investigations support that for cyclic substrates the reactions are proceeding via trans-aminoiridation to form a 5-membered metalacyclic intermediate.

Copper-Catalyzed Asymmetric Allylation of N-Aryl Aldimines.

The copper-catalyzed enantioselective allylation reaction of N-aryl aldimines has been developed using a combination of Cu(OAc)2 and SPINOL-based phosphonamidite. This protocol significantly broadens the substrate scope, such that imines bearing various ortho-substituents on the N-aryl were converted smoothly into homoallylic amines in up to 99% yield and 98% ee. Taking advantage of the diversity of the N-aryl motif, three kinds of N-heterocyclic compounds were constructed, respectively, from the corresponding homoallylic amines in merely one step.

Quinolinamide-Enabled Nickel-Catalyzed Regio- and Diastereoselective γ,δ-Arylalkylation of Nonactivated Alkenes

AbstractA quinolinamide-enabled nickel-catalyzed γ,δ-arylalkylation of homoallylic amines with aryl iodides and organozinc compounds has been developed. The cleavable quinolinamide directing group facilitates the stabilization of a five-membered nickelacycle, and enables the dicarbofunctionalization of nonactivated alkenes with excellently regio-, chemo-, and diastereoselectivity. The reaction with internal alkenes proceeds stereospecifically to provide valuable γ-alkyl-δ-aryl-substituted amines with two vicinal stereocenters. The scope of substrates and the utility of the protocol have been thoroughly studied.

Direct Alkylative Amination using 1-Allylsilatrane.

Homoallylic amines prepared via addition of allylsilanes often require preformed imine substrates, metal catalysts, fluoride activators, or use of protected amines. In this metal-free, air- and water-tolerant procedure, aromatic aldehyde and aniline substrates undergo direct alkylative amination using easily accessible 1-allylsilatrane.

Heterogeneous Single-Atom Zinc on Nitrogen-Doped Carbon Catalyzed Electrochemical Allylation of Imines.

Organometallic reagents are effective for carbon-carbon bond formation; however, consumption of stoichiometric amounts of metals is problematic. We developed electrochemical allylation reactions of imines catalyzed by nitrogen-doped carbon-supported single-atom zinc, which were fixed on a cathode to afford a range of homoallylic amines efficiently. The system could suppress generation of metallic waste, and the catalyst electrode showed advantages over bulk zinc in terms of activity and robustness. An electrochemical flow reaction was also successfully performed to produce the homoallylic amine continuously with minimum amounts of waste.

Alkali-Amide-Catalyzed One-Pot Aminoallylation of Aldehydes with Allylbenzenes.

The deprotonation of allylbenzene was successfully demonstrated with a catalytic alkali amide base (NaN(SiMe3)2). The deprotonated allyl anion could be trapped by in situ generated N-(trimethylsilyl) aldimines to provide value-added homoallylic amines (39 examples, 68-98% yields) in a one-pot manner with excellent liner selectivity. Compared with the previously reported method for the synthesis of homoallylic amines, this method does not need to use the preinstalled protection groups on the imines, which need to be removed after the reaction to obtain the N-H free homoallylic amine derivatives.

Nickel-Catalyzed Enantioselective Electrochemical Reductive Cross-Coupling of Aryl Aziridines with Alkenyl Bromides.

An electrochemically driven nickel-catalyzed enantioselective reductive cross-coupling of aryl aziridines with alkenyl bromides has been developed, affording enantioenriched β-aryl homoallylic amines with excellent E-selectivity. This electroreductive strategy proceeds in the absence of heterogeneous metal reductants and sacrificial anodes by employing constant current electrolysis in an undivided cell with triethylamine as a terminal reductant. The reaction features mild conditions, remarkable stereocontrol, broad substrate scope, and excellent functional group compatibility, which was illustrated by the late-stage functionalization of bioactive molecules. Mechanistic studies indicate that this transformation conforms with a stereoconvergent mechanism in which the aziridine is activated through a nucleophilic halide ring-opening process.

Organocatalytic Asymmetric Synthesis of α‐Trifluoromethyl Homoallylic Amine Derivatives from Trifluoromethyl‐Containing Ketoimines and Isatin‐Derived Morita‐Baylis‐Hillman Carbonates

AbstractThe asymmetric γ‐regioselective‐alkylation reaction which is catalyzed by a chiral tertiary amine ((DHQ)2PHAL) and takes advantage of isatin‐derived Morita‐Baylis‐Hillman carbonates and CF3‐contained ketoimines, delivered chiral α‐trifluoromethylamine derivatives and incorporated an oxindole motif in yields of 65–98%, diastereoselectivities (>20:1 in most cases) and enantioselectivities of 73–99%. The subsequent deprotection gave α‐ trifluoromethyl amines in a stereoselective manner. Furthermore, fused polycyclic frameworks can be furnished by subsequent derivatization of the product without eroding its stereoselectivity.magnified image