A New Reagent System for Modified Ullmann-Type Coupling Reactions: NiCl₂(PPh₃)₂/PPh₃/Zn/NaH/Toluene

A New Reagent System for Modified Ullmann-Type Coupling Reactions:  NiCl2(PPh3)2/PPh3/Zn/NaH/Toluen

Biomimetic Synthesis of Chejuenolides A–C by a Cryptic Lactone-Based Macrocyclization: Stereochemical Implications in Biosynthesis

A hypothetical Mannich macrocyclization in the biosynthesis of chejuenolides A–C served as the basis for the synthetic design herein. Using a lactone-based linear precursor constructed via a tactic sequence of aldol–Julia–aldol reactions on a gram scale, the biomimetic total synthesis and structural validation of chejuenolides A–C were successfully achieved for the first time. The β-oxo-δ-lactone unit in the macrocyclized adducts was fragile and readily converted to a series of C2/C18-diastereoisomers via a decarboxylation and protonation pathway. Stereochemical identification of the biosynthetic precursor (O3P2) confirmed structural adherence to the given macrocycles and previously clarified lankacidins. Moreover, the stereovariants of the linear precursor designed for the macrocyclization event highlighted the unparalleled impact of using this biomimetic approach to determine the stereoselectivity in the proposed enzymatic reaction by reviving the lost or unstable intermediate

Biomimetic Synthesis of Chejuenolides A–C by a Cryptic Lactone-Based Macrocyclization: Stereochemical Implications in Biosynthesis

A hypothetical Mannich macrocyclization in the biosynthesis of chejuenolides A–C served as the basis for the synthetic design herein. Using a lactone-based linear precursor constructed via a tactic sequence of aldol–Julia–aldol reactions on a gram scale, the biomimetic total synthesis and structural validation of chejuenolides A–C were successfully achieved for the first time. The β-oxo-δ-lactone unit in the macrocyclized adducts was fragile and readily converted to a series of C2/C18-diastereoisomers via a decarboxylation and protonation pathway. Stereochemical identification of the biosynthetic precursor (O3P2) confirmed structural adherence to the given macrocycles and previously clarified lankacidins. Moreover, the stereovariants of the linear precursor designed for the macrocyclization event highlighted the unparalleled impact of using this biomimetic approach to determine the stereoselectivity in the proposed enzymatic reaction by reviving the lost or unstable intermediate

Synthetic Study on Tetrapetalones: Stereoselective Cyclization of <i>N</i>-Acyliminium Ion To Construct Substituted 1-Benzazepines

The synthesis of the tetracyclic core of complex antibiotic tetrapetalones has been achieved in three steps starting from the simple intermediate γ-hydroxy amide, which can be accessed through a high-yielding six-step sequence. The successful synthesis relies on a novel strategy based on the N-acyliminium ion cyclization

Biomimetic Synthesis of Chejuenolides A–C by a Cryptic Lactone-Based Macrocyclization: Stereochemical Implications in Biosynthesis

A hypothetical Mannich macrocyclization in the biosynthesis of chejuenolides A–C served as the basis for the synthetic design herein. Using a lactone-based linear precursor constructed via a tactic sequence of aldol–Julia–aldol reactions on a gram scale, the biomimetic total synthesis and structural validation of chejuenolides A–C were successfully achieved for the first time. The β-oxo-δ-lactone unit in the macrocyclized adducts was fragile and readily converted to a series of C2/C18-diastereoisomers via a decarboxylation and protonation pathway. Stereochemical identification of the biosynthetic precursor (O3P2) confirmed structural adherence to the given macrocycles and previously clarified lankacidins. Moreover, the stereovariants of the linear precursor designed for the macrocyclization event highlighted the unparalleled impact of using this biomimetic approach to determine the stereoselectivity in the proposed enzymatic reaction by reviving the lost or unstable intermediate

Biomimetic Synthesis of Chejuenolides A–C by a Cryptic Lactone-Based Macrocyclization: Stereochemical Implications in Biosynthesis

A hypothetical Mannich macrocyclization in the biosynthesis of chejuenolides A–C served as the basis for the synthetic design herein. Using a lactone-based linear precursor constructed via a tactic sequence of aldol–Julia–aldol reactions on a gram scale, the biomimetic total synthesis and structural validation of chejuenolides A–C were successfully achieved for the first time. The β-oxo-δ-lactone unit in the macrocyclized adducts was fragile and readily converted to a series of C2/C18-diastereoisomers via a decarboxylation and protonation pathway. Stereochemical identification of the biosynthetic precursor (O3P2) confirmed structural adherence to the given macrocycles and previously clarified lankacidins. Moreover, the stereovariants of the linear precursor designed for the macrocyclization event highlighted the unparalleled impact of using this biomimetic approach to determine the stereoselectivity in the proposed enzymatic reaction by reviving the lost or unstable intermediate

Biomimetic Synthesis of Chejuenolides A–C by a Cryptic Lactone-Based Macrocyclization: Stereochemical Implications in Biosynthesis

A hypothetical Mannich macrocyclization in the biosynthesis of chejuenolides A–C served as the basis for the synthetic design herein. Using a lactone-based linear precursor constructed via a tactic sequence of aldol–Julia–aldol reactions on a gram scale, the biomimetic total synthesis and structural validation of chejuenolides A–C were successfully achieved for the first time. The β-oxo-δ-lactone unit in the macrocyclized adducts was fragile and readily converted to a series of C2/C18-diastereoisomers via a decarboxylation and protonation pathway. Stereochemical identification of the biosynthetic precursor (O3P2) confirmed structural adherence to the given macrocycles and previously clarified lankacidins. Moreover, the stereovariants of the linear precursor designed for the macrocyclization event highlighted the unparalleled impact of using this biomimetic approach to determine the stereoselectivity in the proposed enzymatic reaction by reviving the lost or unstable intermediate

Synthetic Study on Tetrapetalones: Stereoselective Cyclization of <i>N</i>-Acyliminium Ion To Construct Substituted 1-Benzazepines

The synthesis of the tetracyclic core of complex antibiotic tetrapetalones has been achieved in three steps starting from the simple intermediate γ-hydroxy amide, which can be accessed through a high-yielding six-step sequence. The successful synthesis relies on a novel strategy based on the N-acyliminium ion cyclization

Catalytic Asymmetric Cyanosilylation of Ketones with Chiral Lewis Base

The development of broadly applicable and practical catalytic approaches for the enantioselective creation of quaternary stereocenters remains a highly desirable yet challenging goal. In this Communication, we describe a highly enantioselective cyanosilylation of acetal ketones (α,α-dialkoxy ketones) catalyzed by modified cinchona alkaloids. This reaction is the first highly enantioselective cyanosilylation of ketones catalyzed by an organic chiral Lewis base and is found to be highly efficient with acetal ketones bearing a broad range of alkyl, aryl, alkenyl, and alkynyl substituents. This new catalytic asymmetric reaction, coupled with the versatility of the acetal functionality, provides a broadly useful synthetic method for chiral building blocks bearing quaternary stereocenters. Acetal ketones, readily accessible but previously unexplored in asymmetric synthesis, demonstrate unusual reactivity and selectivity toward the nucleophilic cyanosilylation, thereby suggesting that they may be interesting substrates for other catalytic enantioselective reactions

Synthetic Study on Tetrapetalones: Stereoselective Cyclization of <i>N</i>-Acyliminium Ion To Construct Substituted 1-Benzazepines

The synthesis of the tetracyclic core of complex antibiotic tetrapetalones has been achieved in three steps starting from the simple intermediate γ-hydroxy amide, which can be accessed through a high-yielding six-step sequence. The successful synthesis relies on a novel strategy based on the N-acyliminium ion cyclization