Ytterbium triflate (and trimethylsilyl triflate) catalyzed isomerization of glycidic esters to α-hydroxy-β,γ-unsaturated esters and their conversion into cyclopentanoids using Johnson-Claisen rearrangement

A variety of glycidic esters undergo smooth isomerization to the corresponding α-hydroxy-β, γ-unsaturated esters upon reaction with Yb(OTf)3 or TMSOTf. These α-hydroxy-β, γ-unsaturated esters undergo Johnson-Claisen rearrangement to appropriately substituted diesters, some of which are converted into cyclopentanoids

The addition of morpholine to unsaturated esters

Thesis (M.A.)--Boston University, 1948. This item was digitized by the Internet Archive

SYNTHESIS OF α- HYDROXY-β, γ-UNSATURATED ESTERS: HClO4-SiO2 CATALYZED ISOMERISATION OF GLYCIDIC ESTERS TO α-HYDROXY- β, γ-UNSATURATED ESTERS

α-hydroxy-β, γ-unsaturated esters are important building blocks of bioactive compounds, natural products, achiral and chiral vinyl epoxides. These could be easily obtained by isomerization of glycidic esters. In this paper we have reported easy and convenient way of synthesis of α-hydroxy-β, γ-unsaturated esters by isomerisation of glycidic esters using inexpensive catalyst HClO4-SiO2 and eco-friendly ionic liquid. Moderate to good yields with lower reaction times reported

Influence of Phosphoramidites in Copper-Catalyzed Conjugate Borylation Reaction

Copper(I) has become the preferred metal to catalyze the β-boration of α,β-unsaturated carbonyl compounds, and now we demonstrate that easily accessible monodentate chiral ligands, such as phosphoramidites and phosphites, can be convenient alternative ligands to induce asymmetry in the enantioselective version of this reaction, particularly in the β-boration of α,β-unsaturated imines.

Organocatalytic Lewis base functionalisation of carboxylic acids, esters and anhydrides via C1-ammonium or azolium enolates

This tutorial review highlights the organocatalytic Lewis base functionalisation of carboxylic acids, esters and anhydrides via C1-ammonium/azolium enolates. The generation and synthetic utility of these powerful intermediates is highlighted through their application in various methodologies including aldol-lactonisations, Michael-lactonisations/lactamisations and [2,3]-rearrangements.Publisher PDFPeer reviewe

Hydrazones as Singular Reagents in Asymmetric Organocatalysis

This Minireview summarizes strategies and developments regarding the use of hydrazones as reagents in asymmetric organocatalysis, their distinct roles in nucleophile–electrophile, cycloaddition, and cyclization reactions. The key structural elements governing the reactivity of these reagents in a preferred pathway will be discussed, as well as their different interactions with organocatalysts, leading to diverse activation modes. Along these studies, the synthetic equivalence of N-monoalkyl, N,N-dialkyl, and N-acyl hydrazones with several synthons is also highlighted. Emphasis is also put on the mechanistic studies performed to understand the observed reactivities. Finally, the functional group transformations performed from the available products has also been analyzed, highlighting the synthetic value of these methodologies, which served to access numerous families of valuable multifunctional compounds and nitrogen-containing heterocycles.Ministerio de Economía y Competitividad CTQ2013-48164-C2-1-P, CTQ201348164-C2-2-PEuropean FEDER fundsJunta de Andalucía 2012/FQM 107

Doctor of Philosophy

dissertationGenerally, β,γ-unsaturated carbonyls are thermodynamically less stable than their corresponding α,β-unsaturated isomers. An investigation of SmI2-mediated deconjugation of α,β-unsaturated esters to provide β,γ-unsaturated esters is described herein. Under almost neutral conditions, α,β-unsaturated esters bearing good leaving groups at the γ-position were reductively deconjugated into β,γ-unsaturated esters in excellent yields at low temperature. The newly formed double bonds slightly favored E-geometry, whereas α,β-unsaturated esters bearing poor leaving groups afforded both deconjugated products and saturated products. Bryostatin 1, a macrocyclic lactone isolated from the bryozoan Bugula neritina, has attracted great attention from the scientific community since its structure was identified by Pettit in 1982. Clinical development of bryostatin 1 has been ongoing since 1990. To date, bryostatin 1 has been the subject for various cancers, HIV and Alzheimer’s disease in more than 80 human clinical trials. All the unique bioactivities of bryostatin 1 are closely related to its ability to modulate protein kinase C isozymes (PKCs), which are the key players in cell proliferation and death. Clarifying the structure-activity relationship (SAR) of bryostatin 1 promises extraordinary benefits to our understanding of the detailed mechanism of PKC activation and regulation. The work described herein focuses on the preparation of the C-27 des-methyl bryostatin analogue and its biological evaluation. A convergent and efficient route that involved extension of our pyran-annulation and catalytic asymmetric allylation (CAA) methodologies was developed and successfully delivered the target analogue. Upon addition of a catalytic amount of pyridine, the pyran-annulation reaction was more effective and consistent in terms of its yields. The des-methyl analogue demonstrated that the C-27 had no effect on the binding affinity to PKCs and the biological properties of the molecule. This discovery may facilitate future analogue syntheses. In order to investigate the role of the C-9 hemiketal hydroxyl group in the biological profile of bryostatin 1, a synthetic route was designed to prepare an analogue with the hemiketal alcohol. In this route, SmI2-mediated reductive cyclization was attempted to construct the hydroxypyran A-ring. Unfortunately, a side reaction occurring on the C-ring of the analogue prevented the desired cyclization. Without the cyclized A-ring, an unexpected analogue was finally obtained, which had an expanded macrolactone with a fused C-ring

anti-Selective synthesis of β-boryl-α-amino acid derivatives by Cu-catalysed borylamination of α,β-unsaturated esters

A copper-catalysed regio- and diastereoselective borylamination of α,β-unsaturated esters with B2pin2 and hydroxylamines has been developed to deliver acyclic β-boryl-α-amino acid derivatives with high anti-diastereoselectivity (up to >99 : 1), which is difficult to obtain by the established methods. A chiral phosphoramidite ligand also successfully induces the enantioselectivity, giving the optically active β-borylated α-amino acids. The products can be stereospecifically transformed into β-functionalised α-amino acids, which are of potent interest in medicinal chemistry.Nishino S., Nishii Y., Hirano K.. anti-Selective synthesis of β-boryl-α-amino acid derivatives by Cu-catalysed borylamination of α,β-unsaturated esters. Chemical Science 13, 14387 (2022); https://doi.org/10.1039/d2sc06003e

The Synthesis of Cyclic Enol Ethers via Molybdenum Alkylidene-Catalyzed Ring-Closing Metathesis

An efficient method for the construction of five- and six-membered cyclic vinyl ethers from unsaturated esters using stoichiometric titanium reagents to convert the esters to acyclic olefinic enol ethers which are then transformed to the desired products by catalytic ring-closing olefin metathesis with a molybdenum alkylidene complex is described