Allylic Boronates Research Articles

Transition‐Metal‐Free Borylation of Allylic and Propargylic Alcohols

AbstractThe base‐catalyzed allylic borylation of tertiary allylic alcohols allows the synthesis of 1,1‐disubstituted allyl boronates, in moderate to high yield. The unexpected tandem performance of the Lewis acid–base adduct, [Hbase]+[MeO‐B2pin2]− favored the formation of 1,2,3‐triborylated species from the tertiary allylic alcohols and 1‐propargylic cyclohexanol at 90 °C.

Transition-Metal-Free Borylation of Allylic and Propargylic Alcohols.

The base‐catalyzed allylic borylation of tertiary allylic alcohols allows the synthesis of 1,1‐disubstituted allyl boronates, in moderate to high yield. The unexpected tandem performance of the Lewis acid–base adduct, [Hbase]+[MeO‐B2pin2]− favored the formation of 1,2,3‐triborylated species from the tertiary allylic alcohols and 1‐propargylic cyclohexanol at 90 °C.

Copper-Catalyzed Borylcupration of Allenylsilanes.

A highly regio- and stereoselective copper-catalyzed borylcupration of 1,2-allenylsilanes affords an unexpected regioreversed allylic boronate bearing an extra C-Si bond at the 3-position, with a thermodynamically disfavored Z geometry. Such stereodefined allylic boronates containing an extra alkenyl silane moiety are very useful organodimetallic reagents for organic synthesis.

Copper‐Catalyzed Borylcupration of Allenylsilanes

AbstractA highly regio‐ and stereoselective copper‐catalyzed borylcupration of 1,2‐allenylsilanes affords an unexpected regioreversed allylic boronate bearing an extra C−Si bond at the 3‐position, with a thermodynamically disfavored Z geometry. Such stereodefined allylic boronates containing an extra alkenyl silane moiety are very useful organodimetallic reagents for organic synthesis.

Allylic borylation of tertiary allylic alcohols: a divergent and straightforward access to allylic boronates

A novel method for the preparation of diverse allylic boronates from simple allylic alcohols is reported.

Stereocontrolled Synthesis of Vinyl Boronates and Vinyl Silanes via Atom‐Economical Ruthenium‐Catalyzed Alkene–Alkyne Coupling

AbstractThe synthesis of vinyl boronates and vinyl silanes was achieved by employing a Ru‐catalyzed alkene–alkyne coupling reaction of allyl boronates or allyl silanes with various alkynes. The double bond geometry in the generated vinyl boronates can be remotely controlled by the juxtaposing boron‐ and silicon groups on the alkyne substrate. The synthetic utility of the coupling products has been demonstrated in a variety of synthetic transformations, including iterative cross‐coupling reactions, and a Chan‐Lam‐type allyloxylation followed by a Claisen rearrangement. A sequential one‐pot alkene‐alkyne‐coupling/allylation‐sequence with an aldehyde to deliver a highly complex α‐silyl‐β‐hydroxy olefin with a handle for further functionalization was also realized.

Stereocontrolled Synthesis of Vinyl Boronates and Vinyl Silanes via Atom-Economical Ruthenium-Catalyzed Alkene-Alkyne Coupling.

The synthesis of vinyl boronates and vinyl silanes was achieved by employing a Ru-catalyzed alkene-alkyne coupling reaction of allyl boronates or allyl silanes with various alkynes. The double bond geometry in the generated vinyl boronates can be remotely controlled by the juxtaposing boron- and silicon groups on the alkyne substrate. The synthetic utility of the coupling products has been demonstrated in a variety of synthetic transformations, including iterative cross-coupling reactions, and a Chan-Lam-type allyloxylation followed by a Claisen rearrangement. A sequential one-pot alkene-alkyne-coupling/allylation-sequence with an aldehyde to deliver a highly complex α-silyl-β-hydroxy olefin with a handle for further functionalization was also realized.

Total Synthesis of Solandelactones A and B

AbstractThe total synthesis of solandelactones A and B is presented. The eastern cyclopropyl moiety was prepared following an exceptionally short chemoenzymatic approach whereas enantioselective synthesis of the western side‐chain relied on the application of diastereomerically pure allyl boronates. The natural products solandelactones A and B were isolated in good overall yields following convergence of each eastern and western element by application of the Nozaki–Hiyama–Kishi reaction.

Copper-Catalyzed Cross-Coupling Reaction of Allyl Boron Ester with 1°/2°/3°-Halogenated Alkanes.

The cross-coupling reaction of allyl boron ester with 1°/2°/3°-halogenated alkanes in the presence of copper has been developed for the first time, which provides a mild and efficient method for the construction of saturated C(sp(3))-C(sp(3)) bonds. This protocol shows excellent compatibility with the nonactivated primary, secondary, and even tertiary halogenated alkanes under mild conditions.

ChemInform Abstract: Nonracemic Allylic Boronates Through Enantiotopic‐Group‐Selective Cross‐Coupling of Geminal Bis(boronates) and Vinyl Halides.

AbstractUnder the influence of a chiral palladium catalyst, 1,1‐bis(pinacolboronate) esters undergo asymmetric cross‐coupling with bromoalkenes to generate nonracemic allyl boronates with high levels of enantioselectivity.

ChemInform Abstract: Highly Diastereoselective Generation of Various 3,3‐Disubstituted Allyl Boronates for the Stereospecific Construction of Quaternary Centers.

AbstractVarious dialkyl substituted allyl boronates are condensed with aromatic and aliphatic aldehydes.

Regio- and Chemoselective Diboration of Allenes with Unsymmetrical Diboron: Formation of Vinyl and Allyl Boronic Acid Derivatives

A platinum-catalyzed terminal diboration of 1,1-disubstituted allenes using a differentially protected diboron is described. Diboration occurs in a regio- and chemoselective fashion to furnish vinyl and allyl boronates in good to excellent yield and selectivity. Transformation of the bis-boronyl products to other functional groups as well as in chemoselective cross-coupling is demonstrated.

Nonracemic allylic boronates through enantiotopic-group-selective cross-coupling of geminal bis(boronates) and vinyl halides.

Under the influence of a chiral palladium catalyst, 1,1-bis(pinacolboronate) esters undergo asymmetric cross-coupling with bromoalkenes to generate nonracemic allyl boronates with high levels of enantioselectivity. The so-formed allyl boronates may be oxidized with hydrogen peroxide to provide secondary allylic alcohols or with nitrosobenzene to furnish nonracemic tertiary allylic alcohols. Mechanistic experiments suggest the operation of a pathway involving outer-sphere stereoinvertive transmetalation.

ChemInform Abstract: Catalytic Asymmetric Allylation of Carbonyl Compounds and Imines with Allylic Boronates

AbstractReview: 132 refs.

Synthesis of chiral heterocycles by ligand-controlled regiodivergent and enantiospecific Suzuki Miyaura cross-coupling.

Non-aromatic nitrogen- and oxygen-containing heterocycles such as piperidines and pyrans are prevalent components of natural products and pharmaceutical drugs. Although it has been a workhorse as a synthetic method for assembling unsaturated sp(2)-hybridized substrates, transition metal-catalysed cross-coupling chemistry is traditionally not a suitable approach to prepare chiral non-aromatic heterocycles. Several mechanistic issues hamper the coupling of stereogenic secondary sp(3)-hybridized carbon-metal centres. Moreover, use of unsymmetrical allylic boronates in the Suzuki Miyaura cross-coupling is further complicated by the possibility of forming two regioisomeric products. Here we address this two-pronged problem and demonstrate that chiral enantiomerically enriched heterocyclic allylic boronates can be coupled with high stereochemical retention with a wide variety of aryl and alkenyl halides to independently afford both regioisomeric 2- and 4-substituted dihydropyrans and dehydropiperidines in high selectivity. A divergent mechanism is proposed where regiochemistry is governed by the nature of the ligands on the palladium catalyst. This scalable method is applied to the efficient preparation of the neuroactive alkaloid anabasine and the antidepressant drug paroxetine.

Highly diastereoselective generation of various 3,3-disubstituted allyl boronates for the stereospecific construction of quaternary centers

Single isomer trisubstituted olefins were converted into allyl boron nucleophiles that were condensed with aldehydes to give products containing quaternary centers. The products were obtained in extremely high diastereomeric ratios, a reflection of the stereochemical integrity of the starting materials.

ChemInform Abstract: Activation of Alkynes with B(C6F5)3 — Boron Allylation Reagents Derived from Propargyl Esters.

Novel allyl boron compounds are readily synthesized via rearrangement reactions between Lewis acidic B(C6F5)3 and propargyl esters. These reactions proceed through an initial cyclization followed by ring-opening and concurrent C6F5-group migration. In the absence of disubstitution adjacent to the ester oxygen atom, an allyl boron migration rearrangement leads to formal 1,3-carboboration products. These allyl boron compounds act as allylation reagents with aldehydes introducing both a C3-allyl fragment and a C6F5-unit as a single anti-diastereomer. In these reactions, B(C6F5)3 activates the alkynes, prompting the rearrangement processes and enabling installations of C6F5 and R-groups.

ChemInform Abstract: Synthesis of Tertiary Allylboronates from Vinylboronates.

Allylic boronates are versatile intermediates in organic synthesis. Herein, we present an ‘ate-mediated allylic substitution’ (AMAS) approach to allylic boronates. Bifunctional vinylboroate/ allylic acetate esters react with Grignard reagents to form tertiary ­allylic boronates via an AMAS reaction. We demonstrate that the method tolerates a wide range of substrates and Grignard reagents.

ChemInform Abstract: Enantiospecific, Regioselective Cross‐Coupling Reactions of Secondary Allylic Boronic Esters.

AbstractThe Suzuki‐Miyaura cross‐coupling of enantioenriched secondary allylic boronic esters occurs with high γ‐regioselectivity and high retention of chirality, proceeding via γ‐selective transmetalation and subsequent reductive elimination.

ChemInform Abstract: Preparation of Allylboronates by Pd‐Catalyzed Borylative Cyclization of Dienynes.

AbstractReaction of dienynes (I), (IV), and (VI) with bis(pinacolato)diboron (II) affords allylic boronates (III), (V), and (VII) containing five‐ or six‐membered carbo‐ or heterocycles, by concomitant formation of one C—C and one C—B bond.