Ni-Catalyzed Regioselective Hydroalkoxylation of Branched 1,3-Dienes

Nickel-Catalyzed Enantioconvergent Allenylic Amination of Allenols Activated by Hydrogen-Bonding Interaction with Methanol

The ubiquitous nature of amines in drug compounds, bioactive molecules and natural products has fueled intense interest in their synthesis. Herein, we introduce a nickel-catalyzed enantioconvergent allenylic amination of methanol-activated allenols. This protocol affords a diverse array of functionalized allenylic amines in high yields and with excellent enantioselectivities. The synthetic potential of this method is demonstrated by employing bioactive amines as nucleophiles and conducting gram-scale reactions. Furthermore, mechanistic investigations and DFT calculations elucidate the role of methanol as an activator in the nickel-catalyzed reaction, facilitating the oxidative addition of the C-O bond of allenols through hydrogen-bonding interactions. The remarkable outcomes arise from a rapid racemization of allenols enabled by the nickel catalyst and from highly enantioselective dynamic kinetic asymmetric transformation of η3-alkadienylnickel intermediates.

Nickel-Catalyzed Hydroamination and Hydroalkoxylation of Enelactams with Unactivated Amines and Alcohols

Nickel-catalyzed hydroamination and hydroalkoxylation of enelactams with unactivated amines and alcohols are reported. This method showed good functional group tolerance and delivered the corresponding hydrofunctionalized products in good to excellent yields (≤98%). Furthermore, an intramolecular hydroalkoxylation of an enelactam was also realized, giving a cyclization product in a good yield. Mechanistic studies indicated that tBuI acts as a hydride donor and radical precursor, which is crucial for the success of the reaction.

Palladium-Catalyzed Chemo- and Regioselective C-H Bond Functionalization of Phenols with 1,3-Dienes

Chemo- and site-selective functionalization of phenols offers a rapid strategy for the synthesis of phenol derivatives with diverse structures. Herein, we report a Pd-catalyzed regioselective C-H bond allylic alkylation of phenols with 1,3-dienes, which has precision reactivity at the ortho C-H bond of 2-naphthols, 1-naphthols, and electron-rich phenols. The reaction is accelerated by a diphosphine ligand, does not need any other additive, and features broad substrate scope and good chemo- and regioselectivity. In addition, we have also investigated the asymmetric variant, and the product could be achieved in up to 55% ee.

Catalytic Asymmetric Hydroalkoxylation and Formal Hydration and Hydroaminoxylation of Conjugated Dienes

The straightforward construction of stereogenic centers bearing unprotected functional groups, as in nature, has been a persistent pursuit in synthetic chemistry. Abundant applications of free enantioenriched allyl alcohol and allyl hydroxylamine motifs have made the asymmetric hydration and hydroaminoxylation of conjugated dienes from water and hydroxylamine, respectively, intriguing and efficient routes that have, however, been unachievable thus far. A fundamental challenge is the failure to realize transition-metal-catalyzed enantioselective C-O bond constructions via hydrofunctionalization of conjugated dienes. Here, we perform a comprehensive study toward the stereoselective formal hydration and hydroaminoxylation of conjugated dienes by synthesizing a set of new P,N-ligands and identifying an aryl-derived oxime as a surrogate for both water and hydroxylamine. Asymmetric hydroalkoxylation with new P,N-ligands is also elucidated. Furthermore, versatile derivatizations following hydration provide indirect but concise routes to formal hydrophenoxylation, hydrofluoroalkoxylation, and hydrocarboxylation of conjugated dienes that have been unreported thus far. Finally, a ligand-to-ligand hydrogen transfer process is proposed based on the results of preliminary mechanistic experiments.

Enantioselective Hydroalkoxylation of 1,3-Dienes via Ni-Catalysis

As an advance in hydrofunctionalization, we herein report that alcohols add to 1,3-dienes with high regio- and enantioselectivity. Using Ni-DuPhos, we access enantioenriched allylic ethers. Through the choice of solvent-free conditions, we control the reversibility of C-O bond formation. This work showcases a rare example of methanol as a reagent in asymmetric synthesis.

Ni-Catalyzed Enantioselective Hydrofunctionalizations of 1,3-Dienes

Ni-catalyzed enantioselective hydrofunctionalizations of conjugated dienes are particularly demanding reactions to devise because they require not only addressing the inherent challenges associated with the development of an enantioselective transformation but also overcoming all other aspects of selective catalysis (chemoselectivity, regioselectivity, diastereoselectivity, etc.). However, the value-added nature of the chiral allylic and homoallylic derivatives obtained by these methods, the lack of efficient alternatives, and the use of an earth-abundant first-row transition metal have led to renewed interest over the past decade. In this Perspective, we give an overview of the developments in this field, from the original findings (often dating back to the last century) to the most recent contributions. Emphasis is placed on the nature of the hydrofunctionalization agent (C(sp), C(sp2), C(sp3), N, P, or O).

Enantioselective Selenol-ene Using Rh-Hydride Catalysis

This study showcases the first enantioselective hydroselenation of styrenes. Organoselenium building blocks are accessed with selectivity for the branched isomer. Through a Rh-hydride pathway, C-Se bonds can be forged with excellent regio- and enantiocontrol.

Palladium-Catalyzed Regioselective Intermolecular Hydroalkoxylation of 1-Arylbutadienes

An efficient method for the synthesis of (E)-(3-alkoxybut-1-enyl)benzenes by Pd-catalyzed regioselective intermolecular hydroalkoxylation of 1-arylbutadienes has been developed. This method can be executed in a simple operation with no dry reaction conditions required and having tolerance to a wide range of substrates. Chloromethyl methyl ether (MOMCl) as an additive was found to be essential for the success of the reaction.

Nickel/Brønsted acid dual-catalyzed regioselective C–H bond allylation of phenols with 1,3-dienes

A nickel/Brønsted acid dual-catalyzed C-H bond ortho-allylation of phenols with 1,3-dienes has been developed. This methodology is readily applicable to the modification of complex pharmaceutical molecules.

Access to Highly Stereodefined 1,4-cis-Polydienes by a [Ni/Mg] Orthogonal Tandem Catalytic Polymerization

A [Ni/Mg]-catalyzed orthogonal tandem polymerization has been developed starting from enol phosphates. Initial investigations conducted on branched 1,3-dienes as monomers enabled identification of a Mg-initiated polymerization process leading to 1,4-cis-polydienes. When aryl enol phosphates are used as monomers, the [Ni/Mg]-catalyzed tandem polymerization affords 1,4-cis-polydienes with selectivities up to 99%. Elastomeric or crystalline materials were obtained by simple structural modifications of the monomeric unit. This tandem approach appears as a straightforward and efficient way to enforce diversity and selectivity in diene polymerization while retaining a fair degree of control, just as observed for stepwise systems that are accessible through established time- and manpower-consuming synthetic procedures.

Earth-Abundant 3d Transition Metal Catalysts for Hydroalkoxylation and Hydroamination of Unactivated Alkenes

This review summarizes the most noteworthy achievements in the field of C–O and C–N bond formation by hydroalkoxylation and hydroamination reactions on unactivated alkenes (including 1,2- and 1,3-dienes) promoted by earth-abundant 3d transition metal catalysts based on manganese, iron, cobalt, nickel, copper and zinc. The relevant literature from 2012 until early 2021 has been covered.

[n]Dendralenes as a Platform for Selective Catalysis: Ligand-Controlled Cu-Catalyzed Chemo-, Regio-, and Enantioselective Borylations

We report the development of two complementary methods for the Cu-catalyzed anti-Markovnikov borylation of one specific olefin in 2-substituted [n]dendralenes (n = 3-6). The first protocol operates with a bisphosphine ligand and occurs with high regio- and chemoselectivity for the terminal double bond, independently of the number of cross-conjugated alkenes. We show that the use of a chiral phosphanamine ligand enables the highly chemo-, regio-, and enantioselective borylation of the alkene cross-conjugated with the terminal olefin in [n]dendralenes.

Nickel-catalyzed allyl–allyl coupling reactions between 1,3-dienes and allylboronates

A nickel-hydride catalysis has been developed to facilitate the allyl–allyl cross-coupling reactions between 1,3-dienes and allyl-B(pin) in excellent regioselectivity.