Tandem nucleophilic addition-intramolecular aza-Michael reaction: facile synthesis of chiral fluorinated isoindolines

Fluorinated Imines in Tandem and Cycloaddition Reactions

The chemistry of fluorinated compounds has experienced extraordinary growth in recent decades due to the many and varied properties which many of the compounds that contain fluorinated groups possess. Among all of them, fluorinated chiral imines, in particular the Ellman's imines, are of great importance since they are some of the most interesting building blocks for the synthesis of a large number of enantioenriched carbocycles and heterocycles with extraordinary biological and synthetic properties. This personal account covers the most significant results obtained in our research group in the last two decades concerning asymmetric tandem reactions, paying special attention to the intramolecular aza-Michael reaction (IMAMR), diversity oriented synthesis (DOS), asymmetric tandem reactions involving a p-tolylsulfinyl group as chiral inducer and cycloaddition processes, in particular, the Pauson-Khand reaction, [2+2+2]-cycloadditions and metathesis reactions, starting mainly from enyne compounds and through the use of fluorinated chiral N-sulfinyl imines and their derivatives as starting materials.

Desymmetrization of Cyclohexadienones through Phase-Transfer-Catalyzed Stereoselective Intramolecular Aza-Michael Addition with Chiral Sulfinamide Nucleophiles

This paper reports the desymmetrization of cyclohexadienones through stereoselective intramolecular aza-Michael addition with a tethered chiral sulfinamide nucleophile. The reaction was facilitated by phase-transfer catalysis and produced various nitrogen-containing bicyclic compounds with a yield of up to 93% and a diastereomeric ratio of up to >20:1.

Insight into Stereocontrol in the Asymmetric Intramolecular Allylation with a tert-Butylsulfinamide Nucleophile: Application in the Synthesis of Chiral Isoindoline-1-Carboxylic Acid Esters

The asymmetric induction afforded by a chiral sulfinyl group in a palladium/Brønsted-acid-catalyzed intramolecular allylic amination was investigated. Predictions of the diastereoselectivity for various substrates under assumed total thermodynamic control were obtained from density functional theory (DFT), and the correlation with experimental data demonstrates abrupt changes to kinetic control across the substrate scope. The resulting heterocyclic product was readily converted to valuable isoindoline-1-carboxylic acid esters by a two-step oxidation sequence, providing asymmetric access to a key unnatural α-amino acid scaffold.

KHMDS/Triglyme Cryptate as an Alternative to Phosphazene Base in Stereodivergent Pentafluoroethylation of N-Sulfinylimines Using HFC-125

A protocol for the stereodivergent pentafluoroethylation of N-sulfinylimines using HFC-125 with KHMDS/triglyme has been developed. Both diastereomers of the pentafluoroethylated amines can be selectively synthesized based on the presence or absence of triglyme. This additive-controlled protocol allows the KHMDS/triglyme cryptate to be a straightforward and cheap alternative to previously reported base-controlled stereodivergent trifluoromethylation using potassium hexamethyldisilazide (KHMDS) versus P₄-^tBu.

Palladium/Brønsted-Acid-Catalyzed Diastereoselective Cyclization with Chiral Sulfinamides as Nucleophiles

This article reports diastereoselective cyclization with chiral sulfinamides as nucleophiles in two reaction pathways: (1) intramolecular allylic substitution and (2) sequential aerobic oxidation with aza-Michael addition. These reactions were enabled by synergistic palladium and Brønsted acid catalysis and produced chiral isoindolines with good yields of 55-92% and high diastereoselectivities of 10:1 to >20:1 dr.

Two Decades of Progress in the Asymmetric Intramolecular aza-Michael Reaction

The asymmetric intramolecular aza-Michael reaction (IMAMR) is a very convenient strategy for the generation of heterocycles bearing nitrogen-substituted stereocenters. Due to the ubiquitous presence of these skeletons in natural products, the IMAMR has found widespread applications in the total synthesis of alkaloids and biologically relevant compounds. The development of asymmetric versions of the IMAMR are quite recent, most of them reported in this century. The fundamental advances in this field involve the use of organocatalysts. Chiral imidazolidinones, diaryl prolinol derivatives, Cinchone-derived primary amines and quaternary ammonium salts, and BINOL-derived phosphoric acids account for the success of those methodologies. Moreover, the use of N-sulfinyl imines with a dual role, as nitrogen nucleophiles and as chiral auxiliaries, appeared as a versatile mode of performing the asymmetric IMAMR.

Reagents for Selective Fluoromethylation: A Challenge in Organofluorine Chemistry

The introduction of a monofluoromethyl moiety has undoubtedly become a very important area of research in recent years. Owing to the beneficial properties of organofluorine compounds, such as their metabolic stability, the incorporation of the CH2 F group as a bioisosteric substitute for various functional groups is an attractive strategy for the discovery of new pharmaceuticals. Furthermore, the monofluoromethyl unit is also widely used in agrochemistry, in pharmaceutical chemistry, and in fine chemicals. The problems associated with climate change and the growing need for environmentally friendly industrial processes mean that alternatives to the frequently used CFC and HFBC fluoromethylating agents (CH2 FCl and CH2 FBr) are urgently needed and also required by the Montreal Protocol. This has recently prompted many researchers to develop alternative fluoromethylation agents. This Minireview summarizes both the classical and new generation of fluoromethylating agents. Reagents that act via electrophilic, nucleophilic, and radical pathways are discussed, in addition to their precursors.

Unlocking the direct photocatalytic difluoromethylation of C[double bond, length as m-dash]N bonds

The current study presents a direct CF2H radical addition to C[double bond, length as m-dash]N bonds predicated on the photocatalytic activation of commercially available zinc difluoromethanesulfinate. The mild conditions in place lead to impressive structural diversity, as quinoxalinones and dibenzazepines, among others, are successfully functionalized.

One-Step Diastereoselective Pyrrolidine Synthesis Using a Sulfinamide Annulating Reagent

This communication highlights the use of chiral sulfinamides as nitrogen nucleophiles in intermolecular aza-Michael reactions. When chiral sulfinamides are coupled to a chloroethyl group, the corresponding novel annulating reagents can be used to streamline the stereoselective synthesis of complex pyrrolidine-containing molecules. As a result, it has enabled a medicinal chemistry campaign for the synthesis of biologically active RORγt inverse agonists.

Transition-Metal-Free One-Pot Tandem Synthesis of 3-Ketoisoquinolines from Aldehydes and Phenacyl Azides

An efficient and transition-metal-free strategy for the synthesis of 3-keto-isoquinolines in one pot has been developed from the easily accessible 2-(formylphenyl)acrylates and phenacyl azides. Various substituted aldehydes and phenacyl azides were successfully employed in this transformation to furnish a variety 3-keto-isoquinolines in very good yields. A number of controlled experiments were conducted to postulate the reaction mechanism. Secondary functionalizations of 2-keto-isoquinolins were also performed to showcase the synthetic utility.

Copper Catalyzed One-Pot Three-Component Imination-Alkynylation-aza-Michael Sequence: Enantio- and Diastereoselective Syntheses of 1,3-Disubstituted Isoindolines and Tetrahydroisoquinolines

An enantio- and diastereoselective syntheses of 1, 3-disubstituted isoindolines and tetrahydroisoquinolines via Cu^I-Pybox-diPh catalyzed one-pot imination-alkynylation-aza-Michael sequence has been reported. The three-component reaction produces one C-C and two C-N bonds sequentially with high yield (up to 92%), enantioselectivity (up to 99%), and diastereoselectivity (up to 9:1) in a single operation. Furthermore, the synthetic utility of the product has been demonstrated by LiAlH₄ reduction of ester and hydrogenation of alkyne functionality without losing the stereoselectivity.

Recent advances in the asymmetric synthesis of pharmacology-relevant nitrogen heterocycles via stereoselective aza-Michael reactions

In this review, recent applications of a stereoselective aza-Michael reaction for asymmetric synthesis of naturally occurring N-containing heterocyclic scaffolds and their usefulness to pharmacology are summarized.

Generation of Polar Semi-Saturated Bicyclic Pyrazoles for Fragment-Based Drug-Discovery Campaigns

Synthesising polar semi-saturated bicyclic heterocycles can lead to better starting points for fragment-based drug discovery (FBDD) programs. We report the application of diverse chemistry to construct bicyclic systems from a common intermediate, where pyrazole, a privileged heteroaromatic able to bind effectively to biological targets, is fused to diverse saturated counterparts. The generated fragments can be further developed either after confirmation of their binding pose or early in the process, as their synthetic intermediates. Essential quality control (QC) for selection of small molecules to add to a fragment library is discussed.

Diversity-Oriented Approach to N-Heterocyclic Compounds from α-Phenyl-β-enamino Ester via a Mitsunobu-Michael Reaction Sequence

Herein we delineate a novel route for the diastereoselective construction of diversely substituted N-heterocyclic ring systems as valuable scaffolds for natural products and pharmaceuticals, starting from an easily accessible prochiral α-phenyl-β-enamino ester. The reaction sequence relies on the unexplored reactivity of α-phenyl-β-enamino ester as a nucleophilic partner in the Mitsunobu reaction to forge the N-tethered alkene-alcohol/thiol/amine intermediate, which was subjected to an intramolecular hetero-Michael addition reaction under mild conditions to furnish the respective N-heterocyclic compounds embedded with an exocyclic chiral center in high yields and excellent diastereoselectivities. The methodology is amenable for a broad range of substrates based on a metal-free approach.

Nucleophilic fluoroalkylation/cyclization route to fluorinated phthalides

Discribed in this article is a versatile and practical method for the synthesis of C3-perfluoroalkyl-substituted phthalides in a one-pot manner. Upon treatment of KF or triethylamine, 2-cyanobenzaldehyde reacted with (perfluoroalkyl)trimethylsilanes via nucleophilic addition and subsequent intramolecular cyclization to give perfluoroalkylphthalides in good yields.

Diastereoselective synthesis ofcis-1,3-disubstituted isoindolinesviaa highly site-selective tandem cyclization reaction

A highly site-selective tandem reaction involving regioselective ring opening of aziridines and Michael addition of electron-deficient alkenes has been described.

Recent advances in the synthesis of functionalised monofluorinated compounds

Over the past few years, we have tackled the synthesis of interesting monofluorinated organic molecules, such as: dihydronaphthalene derivatives, β-fluoro sulfones and related carbonyl compounds, fluorohydrins and allylic alcohols.

Asymmetric intramolecular aza-Michael reaction in desymmetrization processes. Total synthesis of hippodamine and epi-hippodamine

The use of chiral sulfinyl amines both as nucleophilic nitrogen sources and chiral inducers has been described for the first time in a desymmetrization-type process involving an intramolecular aza-Michael reaction. The resulting product was employed as an advanced intermediate in the total synthesis of the natural product hippodamine and epi-hippodamine, taking advantage of the special symmetry of these molecules. In addition, this is the first asymmetric total synthesis of epi-hippodamine.

Application of bis(oxazoline) in asymmetric β-amination of chalcones

A variety of β-imidoketone derivatives containing various functional groups were obtained with high enantioselectivities.

Efficient access to enantiopure 1,3-disubstituted isoindolines from selective catalytic fragmentation of an original desymmetrized rigid overbred template

Enantiopure 1,3-disubstituted isoindolines are synthesized from selective C–C bond fragmentation of a rigid overbred template, obtained through an asymmetric desymmetrization reaction.

Asymmetric allylation/Pauson-Khand reaction: a simple entry to polycyclic amines. Application to the synthesis of aminosteroid analogues

Asymmetric allylation of o-iodoarylsulfinylimines has been achieved in high diastereoselectivities. The thus-obtained o-iodoarylhomoallylic sulfinamides participate in a subsequent Sonogashira coupling followed by a diastereoselective intramolecular Pauson-Khand reaction. In this way, tricyclic amines showing a unique benzo-fused indenyl backbone were obtained. The methodology has been applied to the synthesis of amino steroid analogues.