Lewis acid promoted highly diastereoselective Petasis Borono-Mannich reaction: efficient synthesis of optically active β,γ-unsaturated α-amino acids

Strategies for the Development of Asymmetric and Non-Directed Petasis Reactions

The Petasis reaction is a multicomponent reaction of aldehydes, amines and organoboron reagents and is a useful method for the construction of substituted amines. Despite the significant advancement of the Petasis reaction since its invention in 1993, strategies for asymmetric and non-directed Petasis reactions remain limited. To date, there are very few catalytic asymmetric Petasis reactions and almost all asymmetric reports employ a chiral auxiliary. Likewise, the aldehyde component often requires a directing group, ultimately limiting the reaction's scope. In this Concept, key methods for asymmetric and non-directed Petasis reactions are discussed, focusing on how these conceptual advances can be applied to solve long-standing gaps in the Petasis literature.

Cobalt-Catalyzed Selective Hydroboration of 1,3-Enynes with HBpin toward 1,3-Dienylboronate Esters

An efficient cobalt-catalyzed selective hydroboration of 1,3-enynes with HBpin toward 1,3-dienylboronate esters is disclosed. With a commercially available catalytic system of Co(acac)2 and dppf, the hydroboration reactions proceeded well to afford a wide range of 1,3-dienylborates in moderate to high yields. This protocol features a cheap base-metal catalytic system, broad substrate scope, excellent selectivity, easy gram-scale preparation, and good functional group tolerance and provides access to synthetically valuable 1,3-dienylborates.

Recent Trends in the Petasis Reaction: A Review of Novel Catalytic Synthetic Approaches with Applications of the Petasis Reaction

The Petasis reaction, also called the Petasis Borono-Mannich reaction, is a multicomponent reaction that couples a carbonyl derivative, an amine and boronic acids to yield substituted amines. The reaction proceeds efficiently in the presence or absence of a specific catalyst and solvent. By employing this reaction, a diverse range of chiral derivatives can easily be obtained, including α-amino acids. A broad substrate scope, high yields, distinct functional group tolerance and the availability of diverse catalytic systems constitute key features of this reaction. In this review article, attention has been drawn toward the recently reported methodologies for executing the Petasis reaction to produce structurally simple to complex aryl/allyl amino scaffolds.

Diastereo- and regioselective petasis aryl and allyl boration of ninhydrins towards synthesis of functionalized indene-diones and dihydrobenzoindeno-oxazin-ones

Petasis aryl and allyl borations were accomplished using substituted ninhydrins, boronic acids or 2-allyl-4,4,5,5-tetramethyl-1,3,2-dioxaborolane and 1,2-aminophenols in Hexafluoroisopropanol (HFIP) without any catalysts to synthesize different aryl and allyl derivatives of ninhydrins. The nature of substitution in the boronic acids and 1,2-amino phenols was the key factor in determining the diastereo-regioselectivity and the type of product distributions. The products were isolated and characterized by HMBC, HSQC, ¹H, ¹³C NMR experiments and X-ray single crystallographic analysis. A probable reaction pathway involves in situ formation of acyclic and cyclic ninhydrin-amino alcohol adducts, with the positioned hydroxyl group determining the stereo-regioselective outcome via tetracoordinated boron intermediates. A metal free diastereo- and regioselective Petasis aryl and allyl boration of ninhydrins.

Reprogramming natural proteins using unnatural amino acids

Unnatural amino acids have gained significant attention in protein engineering and drug discovery as they allow the evolution of proteins with enhanced stability and activity. The incorporation of unnatural amino acids into proteins offers a rational approach to engineer enzymes for designing efficient biocatalysts that exhibit versatile physicochemical properties and biological functions. This review highlights the biological and synthetic routes of unnatural amino acids to yield a modified protein with altered functionality and their incorporation methods. Unnatural amino acids offer a wide array of applications such as antibody-drug conjugates, probes for change in protein conformation and structure-activity relationships, peptide-based imaging, antimicrobial activities, etc. Besides their emerging applications in fundamental and applied science, systemic research is necessary to explore unnatural amino acids with novel side chains that can address the limitations of natural amino acids.

N-tert-Butanesulfinyl imines in the asymmetric synthesis of nitrogen-containing heterocycles

The synthesis of nitrogen-containing heterocycles, including natural alkaloids and other compounds presenting different types of biological activities have proved to be successful employing chiral sulfinyl imines derived from tert-butanesulfinamide. These imines are versatile chiral auxiliaries and have been extensively used as eletrophiles in a wide range of reactions. The electron-withdrawing sulfinyl group facilitates the nucleophilic addition of organometallic compounds to the iminic carbon with high diastereoisomeric excess and the free amines obtained after an easy removal of the tert-butanesulfinyl group can be transformed into enantioenriched nitrogen-containing heterocycles. The goal of this review is to the highlight enantioselective syntheses of heterocycles involving the use of chiral N-tert-butanesulfinyl imines as reaction intermediates, including the synthesis of several natural products. The synthesis of nitrogen-containing heterocycles in which the nitrogen atom is not provided by the chiral imine will not be considered in this review. The sections are organized according to the size of the heterocycles. The present work will comprehensively cover the most pertinent contributions to this research area from 2012 to 2020. We regret in advance that some contributions are excluded in order to maintain a concise format.

Chiral diene-promoted room temperature conjugate arylation: highly enantioselective synthesis of substituted chiral phenylalanine derivatives and α,α-di(arylmethyl)acetates

A highly enantiocontrolled room temperature rhodium-catalyzed conjugate arylation process was developed. The reaction proceeds through 1,4-addition of α-substituted acrylates followed by enantioselective protonation using a C1-symmetric chiral bicyclo[2,2,2] diene as the ligand and water as the proton source. This exceptionally simple protocol provides a reliable and practical access to structurally important phenylalanine derivatives and α,α-di(arylmethyl)acetates in high yields (up to 99%) with good to excellent ee values (up to 99%).

Petasis vs. Strecker Amino Acid Synthesis: Convergence, Divergence and Opportunities in Organic Synthesis

α-Amino acids find widespread applications in various areas of life and physical sciences. Their syntheses are carried out by a multitude of protocols, of which Petasis and Strecker reactions have emerged as the most straightforward and most widely used. Both reactions are three-component reactions using the same starting materials, except the nucleophilic species. The differences and similarities between these two important reactions are highlighted in this review.

Petasis adducts of tryptanthrin – synthesis, biological activity evaluation and druglikeness assessment

The first example of a tryptanthrin-based Petasis multicomponent reaction is reported, with one of the new derivatives showing moderate fungicidal activity.

Chiral N-tert-Butylsulfinyl Imines: New Discoveries

In this account the reactions of chiral N-tert-butylsulfinyl imines with organometallic reagents such as organoalkaline (lithium, sodium, potassium and cesium derivatives), organomagnesium, organozinc, organoboron, organoaluminium, organoindium and organosilicon compounds is comprehensively described. The reactivity in all cases is derived to synthetic applications in order to prepare interesting organic nitrogenated molecules, especially in the field of alkaloid compounds.

Reactivity and Synthetic Applications of Multicomponent Petasis Reactions

The Petasis boron-Mannich reaction, simply referred to as the Petasis reaction, is a powerful multicomponent coupling reaction of a boronic acid, an amine, and a carbonyl derivative. Highly functionalized amines with multiple stereogenic centers can be efficiently accessed via the Petasis reaction with high levels of both diastereoselectivity and enantioselectivity. By drawing attention to examples reported in the past 8 years, this Review demonstrates the breadth of the reactivity and synthetic applications of Petasis reactions in several frontiers: the expansion of the substrate scope in the classic three-component process; nonclassic Petasis reactions with additional components; Petasis-type reactions with noncanonical substrates, mechanism, and products; new asymmetric versions assisted by chiral catalysts; combinations with a secondary or tertiary transformation in a cascade- or sequence-specific manner to access structurally complex, natural-product-like heterocycles; and the synthesis of polyhydroxy alkaloids and biologically interesting molecules.

Photoredox-Catalyzed Multicomponent Petasis Reaction with Alkyltrifluoroborates

A redox-neutral alkyl Petasis reaction has been developed that proceeds via photoredox catalysis. A diverse set of primary, secondary, and tertiary alkyltrifluoroborates participate effectively in this reaction through a single-electron transfer mechanism, in contrast to the traditional two-electron Petasis reaction, which accommodates only unsaturated boronic acids. This protocol is ideal to diversify benzyl-type and glyoxalate-derived aldehydes, anilines, and alkyltrifluoroborates toward the rapid assembly of libraries of higher molecular complexity important in pharmaceutical and agrochemical settings.

Microwave-assisted nanocatalysis: A CuO NPs/rGO composite as an efficient and recyclable catalyst for the Petasis-borono-Mannich reaction

A CuO NP decorated reduced graphene oxide (CuO NPs/rGO) composite was synthesized and characterized using various analytical techniques viz. XRD, TEM, SEM, UV-Vis, FT-IR, EDX, XPS and CV. The activity of the catalyst was probed for the Petasis-Borono-Mannich (PBM) reaction of boronic acids, salicylaldehydes, and amines under microwave irradiation (MW). The CuO NPs/rGO composite works as a catalyst as well as a susceptor and augments the overall ability of the reaction mixture to absorb MW. The synergistic effect of MW and CuO NPs/rGO resulted in an excellent outcome of the reaction as indicated by the high TOF value (3.64 × 10^-3 mol g^-1 min^-1). The catalytic activity of the CuO NPs/rGO composite was about 12-fold higher under MW compared to the conventional method. The catalyst was recovered by simple filtration and recycled 8 times without significant loss in activity. This atom-economical protocol includes a much milder procedure, and a catalyst benign in nature, does not involve any tedious work-up for purification, and avoids hazardous reagents/byproducts and the target molecules were obtained in good to excellent yields.

Highly enantioselective synthesis of α-tertiary chiral amino acid derivatives through rhodium-catalyzed asymmetric arylation of cyclic N-sulfonyl α-ketimino esters

A simple sulfur-olefin ligand promoted Rh-catalyzed highly enantioselective arylation of cyclic α-ketimino esters with arylboronic acids is described.

Sonochemistry – an innovative opportunity towards a one-pot three-component synthesis of novel pyridylpiperazine derivatives catalysed by meglumine in water

An unprecedented and expeditious synthetic strategy for rapid access to a diversity-oriented library of novel functionalized pyridyl piperazine derivatives is reported.

Palladium-Catalyzed Enantioselective Three-Component Synthesis of α-Arylglycines

A general Pd-catalyzed, enantioselective three-component synthesis of α-arylglycines starting from sulfonamides, glyoxylic acid derivatives, and boronic acids was developed. This operationally straightforward procedure enables the preparation of a wide variety of α-arylglycines in high yields and excellent levels of enantioselectivity from a simple set of readily available starting materials. Incorporation of Pbf-amides gives a racemization-free access to N-unprotected α-arylglycines.

Rapid synthesis of alkylaminophenols via the Petasis borono–Mannich reaction using protonated trititanate nanotubes as robust solid–acid catalysts

The Petasis borono–Mannich reaction was applied to the synthesis of alkylaminophenols from o-hydroxybenzaldehydes, secondary amines and boronic acids in the presence of H₂Ti₃O₇ nanotubes as reusable solid–acid catalysts.

A highly diastereoselective Friedel–Crafts reaction of indoles with isatin-derived N-sulfinyl ketimines towards the efficient synthesis of chiral tetrasubstituted 3-indolyl-3-aminooxindoles

A Lewis acid promoted highly diastereoselective asymmetric Friedel–Crafts alkylation of indoles with isatin-derived N-tert-butanesulfinyl ketimines is described.

Indium-mediated asymmetric intramolecular allenylation of N-tert-butanesulfinyl imines: efficient and practical access to chiral 3-allenyl-4-aminochromanes

An efficient method for the preparation of highly optically active 3-allenyl- and 3-vinyl-4-aminochromanes by In-mediated intramolecular cyclization has been developed. The synthetic utilities of the approach were demonstrated by the construction of various chiral polycyclic heterocycles, especially the interesting spiroheterocyclic compound 9 and steroid analogue 10.

Lewis acid promoted diastereoselective addition of TMSCN and TMSCF3 to isatin-derived N-sulfinyl ketimines: synthesis of optically active tetrasubstituted 3-aminooxindoles

A practical and efficient method for preparation of highly enantiomerically enriched 3-cyano-3-aminooxindoles and 3-trifluoromethyl-3-aminooxindoles with up to 99% optical purity by a Lewis acid promoted diastereoselective Strecker reaction and trifluoromethylation of isatin-derived N-tert-butanesulfinyl ketimines has been developed. This protocol allows direct use of N-free isatin substrates under mild conditions.

Simple sulfur–olefins as new promising chiral ligands for asymmetric catalysis

Recent progress on exploring sulfur-containing hybrid olefins as new elegant ligands for enantioselective catalytic processes is surveyed.

Synthesis of tertiary propargylamines via a rationally designed multicomponent reaction of primary amines, formaldehyde, arylboronic acids and alkynes

A novel approach for the synthesis of tertiary propargylamines is achieved through a Cu(OAc)₂-catalyzed multicomponent reaction of primary amines, formaldehyde, arylboronic acids and alkynes.

Regio- and stereocontrolled access to γ-boronated unsaturated amino esters and derivatives from (Z)-alkenyl 1,2-bis(boronates)

The Borono-Mannich reaction of (Z)-1-alkene-1,2-diboronic esters proceeded regioselectively at the terminal C-B bond to afford (E)-γ-boronated unsaturated amino esters in good yields. These compounds were then subjected to Suzuki couplings for the creation of diversely substituted olefinic amino acid systems. Several other functional transformations were also carried out to illustrate the synthetic utility of the Petasis products.

Titanium-mediated reductive cross-coupling reactions of imines with terminal alkynes: An efficient route for the synthesis of stereodefined allylic amines

Low-valency titanium species, generated in situ by using Ti(OiPr)₄/2 c-C₅H₉MgCl reagent, react with imines to give a titanium-imine complex that can couple with terminal alkynes to provide azatitanacyclopentenes with excellent regioselectivity. Stereodefined allylic amines are obtained in good yields after hydrolysis or iodonolysis of the corresponding azatitanacyclopentenes. When ethynylcyclopropane is used as the coupling partner to react with imines in this reaction, the initially generated allylic amine undergoes an unexpected 1,3-amino migration on silica gel during the column chromatography.