Copper(I)-Catalyzed Enantioselective Nucleophilic Borylation of Aldehydes: An Efficient Route to Enantiomerically Enriched α‑Alkoxyorganoboronate Esters

The first catalytic enantioselective nucleophilic borylation of a CO double bond has been achieved. A series of aldehydes reacted with a diboron reagent in the presence of a copper­(I)/DTBM-SEGPHOS complex catalyst using MeOH as a proton source to give the corresponding optically active α-alkoxyorganoboronate esters with excellent enantioselectivities. Furthermore, the products could be readily converted to the corresponding functionalized chiral alcohol derivatives through stereospecific C–C bond forming reactions involving the stereogenic C–B bond

Copper(I)-Catalyzed Borylative <i>exo</i>-Cyclization of Alkenyl Halides Containing Unactivated Double Bond

A borylative <i>exo</i>-cyclization of alkenyl halides has been reported. The reaction includes the regioselective addition of a borylcopper­(I) intermediate to unactivated terminal alkenes, followed by the intramolecular substitution of the resulting alkylcopper­(I) moiety for the halide leaving groups. Experimental and theoretical investigations of the reaction mechanism have also been described. This reaction provides a new method for the synthesis of alkylboronates containing strained cycloalkyl structures from simple starting materials

Silicon-Tethered Strategy for Copper(I)-Catalyzed Stereo- and Regioselective Alkylboration of Alkynes

Stereoselective silicon-tethered alkylboration of alkynes in the presence of a copper­(I) catalyst and a diboron reagent provided the corresponding cyclic alkenylboronates in high yields (up to 99% yield) with excellent regio- and <i>syn</i>-selectivities (<i>E</i>/<i>Z</i> = <1:99). The products, which can be considered as the formal alkyne intermolecular alkylboration products, undergo subsequent selective derivatization, including ring opening, to give functionalized <i>trans</i>-stilbene derivatives

Anomalous Reactivity of Silylborane: Transition-Metal-Free Boryl Substitution of Aryl, Alkenyl, and Alkyl Halides with Silylborane/Alkoxy Base Systems

An unexpected borylation of organic halides with a silyborane in the presence of an alkoxy base has been observed. This formal nucleophilic boryl substitution can be applied to a broad range of substrates with high functional group compatibility. Even sterically hindered aryl bromides afforded the corresponding boryl compounds in high yields. Preliminary mechanistic studies indicated that this boryl substitution is promoted by neither transition-metal contamination nor a radical-mediated process

Copper(I)-Catalyzed Enantioselective Synthesis of α‑Chiral Linear or Carbocyclic (<i>E</i>)‑(γ-Alkoxyallyl)boronates

A new method has been developed for the catalytic asymmetric synthesis of α-chiral linear or carbocyclic (γ-alkoxyallyl)­boronates via the copper­(I)-catalyzed γ-boryl substitution of allyl acetals. This reaction afforded the products in high yields with excellent E:Z selectivities and enantioselectivities [only (E)-product, 91–98% ee] and also exhibited high functional group compatibility. Subsequent allylation of aldehydes with the α-chiral (γ-alkoxyallyl)­boronates provided the anti-1,2-diol derivatives in a highly stereospecific manner, and the utility of the α-chiral (γ-alkoxyallyl)­boronates was further demonstrated by a convergent coupling of a complex polyol derivative using a (γ-alkoxyallyl)­boronate and a chiral α-oxyaldehyde. The stereoselective modular construction of a complex 3,3-disubstituted cyclopentene containing three consecutive stereocenters including a quaternary chiral carbon was also reported. Useful transformations of the α-chiral linear (γ-alkoxyallyl)­boronates were also demonstrated

Copper(I)-Catalyzed Enantioselective Synthesis of α‑Chiral Linear or Carbocyclic (<i>E</i>)‑(γ-Alkoxyallyl)boronates

A new method has been developed for the catalytic asymmetric synthesis of α-chiral linear or carbocyclic (γ-alkoxyallyl)­boronates via the copper­(I)-catalyzed γ-boryl substitution of allyl acetals. This reaction afforded the products in high yields with excellent E:Z selectivities and enantioselectivities [only (E)-product, 91–98% ee] and also exhibited high functional group compatibility. Subsequent allylation of aldehydes with the α-chiral (γ-alkoxyallyl)­boronates provided the anti-1,2-diol derivatives in a highly stereospecific manner, and the utility of the α-chiral (γ-alkoxyallyl)­boronates was further demonstrated by a convergent coupling of a complex polyol derivative using a (γ-alkoxyallyl)­boronate and a chiral α-oxyaldehyde. The stereoselective modular construction of a complex 3,3-disubstituted cyclopentene containing three consecutive stereocenters including a quaternary chiral carbon was also reported. Useful transformations of the α-chiral linear (γ-alkoxyallyl)­boronates were also demonstrated

Theoretical Mechanistic Investigation of the Dynamic Kinetic Resolution of N‑Protected Amino Acid Esters using Phase-Transfer Catalysts

A detailed theoretical mechanistic investigation on the dynamic kinetic resolution of N-protected amino acid esters using phase-transfer catalysts is described. Semiautomatic exhaustive conformation search of transition state (TS)-like structures were carried out using the ConFinder program and the pseudo-TS conformational search (PTSCS) method. This conformational search method successfully provided reasonable TS structures for determining the stereoselectivity in the asymmetric base hydrolysis of hexafluoroisopropyl (HFIP) esters as well as the racemization mechanism. Furthermore, the independent gradient model (IGM) analysis of the TS structures suggested that the H-bonding interactions with the oxyanion hole and π-stacking interactions are the common important features of the proposed TS structures that determine the stereoselectivity

Decomposition of effect of cluster-mean centered self-included model (2a) and its re-parameterized form (2b).

a<p>As explained in the main text, <i>y_ij</i> is an observed outcome of individual <i>i</i> in group <i>j</i>, <i>x_ij</i> is an individual-level social capital score of individual <i>i</i> in group <i>j</i>,  =  is the mean of social capital scores of all individuals in group <i>j</i>, <i>n_j</i> is the size of the group <i>j</i>, and  =  is the mean of social capital scores of all individuals (excluding individual <i>i</i>) in group <i>j</i>.</p>b<p>This effect is also known as between-cluster effect.</p>c<p>This effect is also known as within-cluster effect.</p

Theoretical Mechanistic Investigation of the Dynamic Kinetic Resolution of N‑Protected Amino Acid Esters using Phase-Transfer Catalysts

A detailed theoretical mechanistic investigation on the dynamic kinetic resolution of N-protected amino acid esters using phase-transfer catalysts is described. Semiautomatic exhaustive conformation search of transition state (TS)-like structures were carried out using the ConFinder program and the pseudo-TS conformational search (PTSCS) method. This conformational search method successfully provided reasonable TS structures for determining the stereoselectivity in the asymmetric base hydrolysis of hexafluoroisopropyl (HFIP) esters as well as the racemization mechanism. Furthermore, the independent gradient model (IGM) analysis of the TS structures suggested that the H-bonding interactions with the oxyanion hole and π-stacking interactions are the common important features of the proposed TS structures that determine the stereoselectivity

Reaction Mechanism of the Anomalous Formal Nucleophilic Borylation of Organic Halides with Silylborane: Combined Theoretical and Experimental Studies

Theoretical and experimental studies have been conducted to elucidate the mechanism of the formal nucleophilic boryl substitution of aryl and alkyl bromides with silylborane in the presence of potassium methoxide. Density functional theory was used in conjunction with the artificial force induced reaction method in the current study to determine the mechanism of this reaction. The results of this analysis led to the identification of a unique carbanion-mediated mechanism involving the halogenophilic attack of a silyl nucleophile on the bromine atom of the substrate. These calculations have, therefore, provided a mechanistic rationale for this counterintuitive borylation reaction. Furthermore, the good functional group compatibility and high reactivity exhibited by this reaction toward sterically hindered substrates can be understood in terms of the low activation energy required for the reaction of the silyl nucleophile with the bromine atom of the substrate and the subsequent rapid and selective consumption of the carbanion species by the in situ generated boron electrophile. The results of an experimental study involving the capture of the anion intermediate provided further evidence in support of the generation of a carbanion species during the course of this reaction. The anomalous formal nucleophilic borylation mechanism reported in this study could be used to provide new insights into silicon and boron chemistry