Decarboxylative borylation

SuFEx Click Chemistry Enabled Late-Stage Drug Functionalization

Sulfur(VI) Fluoride Exchange (SuFEx) is a new family of click chemistry transformations which relies on readily available materials to produce compounds bearing the S^VI-F motif. The potential of SuFEx in drug discovery has just started to be explored. We report the first method of SuFEx chemistry for the conversion of phenolic compounds to their respective arylfluorosulfate derivatives in situ in 96-well plates. This method is compatible with automated synthesis and screening to quickly assess the biological activities of the in situ generated, crude products. Using this method, we perform late-stage functionalization of a panel of known anticancer drugs to generate the corresponding arylfluorosulfates. These in situ generated arylfluorosulfates are directly tested in a cancer-cell growth inhibition assay in parallel with their phenolic precursors. We discover three arylfluorosulfates that exhibit improved anticancer cell proliferation activities compared to their phenol precursors. Among these three compounds, the fluorosulfate derivative of Fulvestrant possesses significantly enhanced activity to down-regulate estrogen receptor (ER) expression in ER⁺ breast cancer cell line MCF-7 and the fluorosulfate derivative of Combretastatin A4-a general anticancer drug currently being evaluated under clinical trials-exhibits a 70-fold increase in potency in the drug resistant colon cancer cell line HT-29.

2-Azadienes as Reagents for Preparing Chiral Amines: Synthesis of 1,2-Amino Tertiary Alcohols by Cu-Catalyzed Enantioselective Reductive Couplings with Ketones

We introduce a new strategy for synthesis of chiral amines: couplings of α-aminoalkyl nucleophiles generated by enantioselective migratory insertion of 2-azadienes to a Cu-H. In this report, we demonstrate its application in catalytic reductive coupling of 2-azadienes and ketones to furnish 1,2-amino tertiary alcohols with vicinal stereogenic centers.

Photoredox-Catalyzed Decarboxylative Alkylation of Silyl Enol Ethers To Synthesize Functionalized Aryl Alkyl Ketones

Photoredox-catalyzed decarboxylative alkylation of silyl enol ethers has been developed. Diverse functionalized aryl alkyl ketones were afforded in modest to good yields using N-(acyloxy)phthalimide as an easy access alkyl radical source under mild and operationally simple conditions. The excellent performance of drug molecules such as fenbufen and indomethacin and naturally occurring carboxylic acids such as stearic acid and dehydrocholic acid further demonstrated the practicability of the reaction.

Visible-light-mediated allylation of alkyl radicals with allylic sulfones via a deaminative strategy

A mild and simple protocol is developed for the synthesis of terminal alkenes via site-specific C–C bond formation upon visible-light irradiation.

A solid-phase approach for the synthesis of α-aminoboronic acid peptides

A solid-phase synthesis of α-aminoboronic acid peptides using a 1-glycerol polystyrene resin is described.

A Lewis Base Catalysis Approach for the Photoredox Activation of Boronic Acids and Esters

We report herein the use of a dual catalytic system comprising a Lewis base catalyst such as quinuclidin-3-ol or 4-dimethylaminopyridine and a photoredox catalyst to generate carbon radicals from either boronic acids or esters. This system enabled a wide range of alkyl boronic esters and aryl or alkyl boronic acids to react with electron-deficient olefins via radical addition to efficiently form C-C coupled products in a redox-neutral fashion. The Lewis base catalyst was shown to form a redox-active complex with either the boronic esters or the trimeric form of the boronic acids (boroxines) in solution.

Nickel-catalyzed acetamidation and lactamization of arylboronic acids

A nickel-catalyzed acetamidation and lactamization of arylboronic acids via a one-pot reaction with ynamides and N-hydroxyphthalimide is described. This protocol features with mild reaction conditions and a broad substrate scope, and has been successfully applied to late-stage functionalization of pharmaceuticals. Moreover, control reactions were conducted to elucidate a plausible mechanism.

Decarboxylative Alkynylation

The development of a new decarboxylative cross-coupling method that affords terminal and substituted alkynes from various carboxylic acids is described using both nickel- and iron-based catalysts. The use of N-hydroxytetrachlorophthalimide (TCNHPI) esters is crucial to the success of the transformation, and the reaction is amenable to in situ carboxylic acid activation. Additionally, an inexpensive, commercially available alkyne source is employed in this formal homologation process that serves as a surrogate for other well-established alkyne syntheses. The reaction is operationally simple and broad in scope while providing succinct and scalable avenues to previously reported synthetic intermediates.

Deaminative Strategy for the Visible-Light-Mediated Generation of Alkyl Radicals

A deaminative strategy for the visible-light-mediated generation of alkyl radicals from redox-activated primary amine precursors is described. Abundant and inexpensive primary amine feedstocks, including amino acids, were converted in a single step into redox-active pyridinium salts and subsequently into alkyl radicals by reaction with an excited-state photocatalyst. The broad synthetic potential of this protocol was demonstrated by the alkylation of a number of heteroarenes under mild conditions.

Practical, efficient, and broadly applicable synthesis of readily differentiable vicinal diboronate compounds by catalytic three-component reactions

A practical, efficient and broadly applicable catalytic method for synthesis of easily differentiable vicinal diboronate compounds is presented. Reactions are promoted by a combination of PCy3 or PPh3, CuCl and LiOt-Bu and may be performed with readily accessible alkenyl boronate substrates. Through the use of an alkenyl-B(pin) (pin = pinacolato) or alkenyl- B(dan) (dan = naphthalene-1,8-diaminato) starting material and commercially available (pin)B- B(dan) or B2(pin)2 as the reagent, a range of vicinal diboronates, including those that contain a B-substituted quaternary carbon center, may be prepared in up to 91% yield and with >98% site selectivity. High enantioselectivities can be obtained (up to 96:4 er) through the use of commercially available chiral bis-phosphine ligands for reactions that afford mixed diboronate products.

Pd-Catalyzed Decarbonylative Cross-Couplings of Aroyl Chlorides

This report describes a method for Pd-catalyzed decarbonylative cross-coupling that enables the conversion of carboxylic acid derivatives to biaryls, aryl amines, aryl ethers, aryl sulfides, aryl boronate esters, and trifluoromethylated arenes. The success of this transformation leverages the Pd0/Brettphos-catalyzed decarbonylative chlorination of aroyl chlorides, which can then participate in diverse cross-coupling reactions in situ using the same Pd catalyst.

Residue-Specific Peptide Modification: A Chemist's Guide

Advances in bioconjugation and native protein modification are appearing at a blistering pace, making it increasingly time consuming for practitioners to identify the best chemical method for modifying a specific amino acid residue in a complex setting. The purpose of this perspective is to provide an informative, graphically rich manual highlighting significant advances in the field over the past decade. This guide will help triage candidate methods for peptide alteration and will serve as a starting point for those seeking to solve long-standing challenges.

Enabling the Cross-Coupling of Tertiary Organoboron Nucleophiles through Radical-Mediated Alkyl Transfer

The construction of quaternary centers is a common challenge in the synthesis of complex materials and natural products. Current cross-coupling strategies that can be generalized for setting these centers are sparse and, when known, are typically predicated on the use of reactive organometallic reagents. To address this shortcoming a new, photoredox-Ni dual catalytic strategy for the cross-coupling of tertiary organoboron reagents with aryl halides is reported. In addition to details on the cross-coupling scope and limitations, full screening efforts and mechanistic experiments are communicated.

Decarboxylative Borylation of Aliphatic Esters under Visible-Light Photoredox Conditions

The conventional methods for preparing alkyl boronates often necessitate anhydrous and demanding reaction conditions. Herein, a new, operationally simple decarboxylative borylation reaction of readily available aliphatic acid derivatives under additive-free visible-light photoredox conditions in nonanhydrous solvents has been described. Primary and secondary alkyl boronates or tetrafluoroborates with various functional groups were prepared accordingly. A catalytic cycle involving alkyl radical reaction with base-activated diboron species has been proposed.