Alkenylboron Reagents Research Articles

The reactivity of alkenyl boron reagents in catalytic reactions: recent advances and perspectives

Recent advances focusing on novel reactivity of alkenyl boron reagents in polar or radical pathways within catalytic reactions by employing transition metal catalysis, organocatalysis have been summarized and discussed.

Synthesis and Palladium-Catalyzed Cross-Coupling of an Alkyl-Substituted Alkenylboronic Acid Pinacol Ester with Aryl Bromides

The palladium-catalyzed cross-coupling reaction of alkyl-substituted alkenylboron reagents with aryl halides is a versatile method to introduce a hydrophobic hydrocarbon chain onto organic compounds of interest. The application of the cross-coupling reaction is enabled by synthetic methods for the preparation of alkenylboron reagents. The geometrically pure, alkyl-substituted alkenylboron reagent, (E)-octenylboronic acid pinacol ester, was prepared by 9-BBN-catalyzed hydroboration reaction of 1-octene with pinacolborane in refluxing 1 M THF solution. This reagent was then evaluated in palladium-catalyzed cross-coupling reactions with aryl bromides. The highest yield of the (E)-1-phenyloctene was obtained when SPhos was used as the ligand, K2CO3 was used as the base, and DMF was used as the reaction solvent. Other electron-rich, electron-poor, sterically hindered, and heteroaromatic substrates produced the corresponding (E)-1-phenyloctene derivatives in moderate to good yield. KEYWORDS: Organic synthesis; Aryl alkene synthesis; Palladium-catalyzed cross-coupling; Suzuki-Miyaura reaction; Stereocontrolled alkene preparation; Hydroboration; 9-Borobicyclo[3.3.1]nonane; Reaction optimization

Enantioselective Radical Addition/Cross‐Coupling of Organozinc Reagents, Alkyl Iodides, and Alkenyl Boron Reagents

AbstractA hybrid transition‐metal/radical process is described that results in the addition of organozinc reagents and alkyl halides across alkenyl boron reagents in an enantioselective catalytic fashion. The reaction can be accomplished both intermolecularly and intramolecularly, providing useful product yields and high enantioselectivities in both manifolds.

Enantioselective Radical Addition/Cross-Coupling of Organozinc Reagents, Alkyl Iodides, and Alkenyl Boron Reagents.

A hybrid transition-metal/radical process is described that results in the addition of organozinc reagents and alkyl halides across alkenyl boron reagents in an enantioselective catalytic fashion. The reaction can be accomplished both intermolecularly and intramolecularly, providing useful product yields and high enantioselectivities in both manifolds.

Stereoselective Synthesis of Trisubstituted Alkenylboron Reagents by Boron-Wittig Reaction of Ketones.

Application of the boron-Wittig reaction to ketone electrophiles provides a straightforward route to trisubstituted alkenylboronic esters. With either a pentamethyldiethylenetriamine or trimethyl-1,4,7-triazacyclononane additive, the olefination can occur with very high levels of stereocontrol and in good chemical yield.

ChemInform Abstract: Synthesis of α,α‐Difluoromethylene Alkynes by Palladium‐Catalyzed gem‐Difluoropropargylation of Aryl and Alkenyl Boron Reagents.

AbstractThe Pd‐catalyzed coupling of difluoropropargyl bromides (I) and (IV) with arylboronic acids (II) is reported for the first time.

Synthesis of α,α‐Difluoromethylene Alkynes by Palladium‐Catalyzed gem‐Difluoropropargylation of Aryl and Alkenyl Boron Reagents

gem-Difluoropropargyl bromides are versatile intermediates in organic synthesis, but have rarely been employed in transition-metal-catalyzed cross-coupling reactions. The first palladium-catalyzed gem-difluoropropargylation of organoboron reagents with gem-difluoropropargyl bromides is now reported. The reaction proceeds under mild reaction conditions with high regioselectivity; it features a broad substrate scope and excellent functional-group compatibility and thus provides an attractive approach for the synthesis of complex fluorinated molecules, in particular for drug discovery and development.

Synthesis of α,α‐Difluoromethylene Alkynes by Palladium‐Catalyzed gem‐Difluoropropargylation of Aryl and Alkenyl Boron Reagents

Abstractgem‐Difluoropropargyl bromides are versatile intermediates in organic synthesis, but have rarely been employed in transition‐metal‐catalyzed cross‐coupling reactions. The first palladium‐catalyzed gem‐difluoropropargylation of organoboron reagents with gem‐difluoropropargyl bromides is now reported. The reaction proceeds under mild reaction conditions with high regioselectivity; it features a broad substrate scope and excellent functional‐group compatibility and thus provides an attractive approach for the synthesis of complex fluorinated molecules, in particular for drug discovery and development.

Stereospecific Cross-Coupling between Alkenylboronates and Alkyl Halides Catalyzed by Iron–Bisphosphine Complexes

A stereospecific and high-yielding cross-coupling reaction between alkenylboron reagents and alkyl halides is described. The reaction has been achieved by using well-defined iron-bisphosphine complexes such as 1b FeCl(2)(3,5-t-Bu(2)-SciOPP), which was recently developed by the authors' group. Various nonactivated alkyl bromides and chlorides possessing a base/nucleophile-sensitive functional group can participate in the cross-coupling, demonstrating its utility for stereoselective synthesis of functional molecules bearing a carbon-carbon double bond.

ChemInform Abstract: Catalytic Enantioselective Synthesis of Secondary Allylic Alcohols from Terminal Alkynes and Aldehydes via 1‐Alkenylboron Reagents.

A practical one-pot method has been developed for preparing enantioenriched secondary allylic alcohols starting from terminal alkynes and aldehydes. Hydroboration of terminal alkynes with dicyclohexylborane and subsequent reaction of the resulting alkenylboron reagents with aldehydes in the presence of a catalytic amount (5 mol %) of 3-(3,5-diphenylphenyl)-H8-BINOL and excess titanium tetraisopropoxide afforded the corresponding allylic alcohols in high enantioselectivities up to 94% ee.

Titanium-Catalyzed Reaction of Alkenylboron Reagents with Aldehydes

Titanium-Catalyzed Reaction of Alkenylboron Reagents with Aldehydes

Catalytic Enantioselective Synthesis of Secondary Allylic Alcohols from Terminal Alkynes and Aldehydes via 1-Alkenylboron Reagents

A practical one-pot method has been developed for preparing enantioenriched secondary allylic alcohols starting from terminal alkynes and aldehydes. Hydroboration of terminal alkynes with dicyclohexylborane and subsequent reaction of the resulting alkenylboron reagents with aldehydes in the presence of a catalytic amount (5 mol %) of 3-(3,5-diphenylphenyl)-H(8)-BINOL and excess titanium tetraisopropoxide afforded the corresponding allylic alcohols in high enantioselectivities up to 94% ee.

Exploring Rhodium-Catalysed Conjugate Addition of Chiral Alkenylboronates Using Chiral Olefin Ligands

The rhodium-catalysed addition of chiral alkenylboron reagents to prochiral α,β-unsaturated carbonyl acceptors are demonstrated to proceed under ligand control. The highest activities were obtained with chiral olefin ligands and the configuration of the new stereocentre can be predicted by using established models.

Asymmetric Synthesis of α-Branched Allylic Amines by the Rh(I)-Catalyzed Addition of Alkenyltrifluoroborates to N-tert-Butanesulfinyl Aldimines

The first Rh(I)-catalyzed addition of alkenylboron reagents to imines is described. The Rh(I)-catalyzed addition of potassium alkenyltrifluoroborate salts to both aromatic and aliphatic N-tert-butanesulfinyl aldimines proceeds in good yields (up to 97%) and with very high diastereoselectivities (95:5 to >99:1). This new method enables the general and efficient asymmetric synthesis of the important class of alpha-branched allylic amines from readily available and stable starting materials.

Rhodium-catalyzed asymmetric addition of aryl- and alkenylboron reagents to electron-deficient olefins

Abstract Asymmetric 1,4-arylation and -alkenylation was achieved by use of organoboronic acids or their derivatives in the presence of a rhodium catalyst coordinated with binap or its related ligands. The scope of this asymmetric addition is very broad, α, β-unsaturated ketones, esters, amides, 1-alkenylphosphonates, and 1-nitroalkenes being efficiently converted into the corresponding 1,4-addition products with over 95% enantioselectivity. The catalytic cycle in water is proposed to involve three intermediates [aryl-or alkenyl-rhodium (oxa-π-allyl) rhodium, and hydroxo-rhodium] by NMR studies on the rhodium intermediates.