Ring expansion of epoxides under Brønsted base catalysis: formal [3+2] cycloaddition of β,γ-epoxy esters with imines providing 2,4,5-trisubstituted 1,3-oxazolidines

SnCl2-catalyzed multicomponent coupling: synthesis of 1,3-oxazolidine derivatives using paraformaldehyde as a C1 feedstock

SnCl2 catalyzed the three-component coupling of aniline, epoxide, and paraformaldehyde, resulting in the synthesis of 1,3-oxazolidine derivatives. The reaction is simple and does not require any additives, bases, or oxidants, and proceeds at moderate temperature with good functional group tolerance. The scope of the utilization of paraformaldehyde as the methylene source was further extended to the synthesis of benzothiazole and 4,4'-methylenebis(N,N-dimethylaniline) using the same catalyst. A catalytic pathway was proposed based on the control experiments.

Cycloaddition of N-arylnitrones with donor-acceptor oxiranes via C-C bond cleavage to construct 1,5,2-dioxazinanes

Highly functionalized 1,5,2-dioxazinanes could be smoothly produced via a Sc(OTf)3-catalyzed chemoselective [3 + 3] cycloaddition of various N-arylnitrones with a series of donor-acceptor oxiranes. This reaction involves in situ generation of 1,3-dipoles through Sc(OTf)3-catalyzed C-C bond cleavage of oxiranes and moderate to high yields were obtained for most substrates. This transformation features C-C bond cleavage of donor-acceptor oxiranes, accessible starting materials and mild reaction conditions.

Synthesis and Evaluation of 18F-Labeled Boramino Acids as Potential New Positron Emission Tomography Agents for Cancer Management

Boron neutron capture therapy (BNCT) is a promising cancer treatment strategy that utilizes boron-containing ligands. In this report, a series of substituted boramino acids were synthesized and evaluated, aiming to obtain metabolically stable boron-derived agents that could integrate positron emission tomography (PET) with BNCT (a theranostic agent). Based on the phenylalanine (Phe) core structure, the impact of substitution groups on tumor accumulation was studied. The agents were labeled with fluorine-18 in 27.2-66.8% yield via the ¹⁸F-¹⁹F isotope exchange reaction. In B16-F10 tumor-bearing mice, [¹⁸F]-(R)-(1-ammonio-2-(4-methoxyphenyl) ethyl) trifluoroborate (R-[¹⁸F]-5a) demonstrated the best tumor uptake (5.54 ± 2.32% ID/g based on ex vivo biodistribution and 3.5 ± 0.04% ID/g based on PET imaging with the tumor-to-muscle ratio up to 2.6) and stability compared with other tested agents. Together, R-[¹⁸F]-5a is a promising agent that could potentially integrate PET and BNCT, whose treatment efficacy is worth further evaluation in the future.

Cu-catalyzed asymmetric addition of alcohols to β,γ-alkynyl-α-imino esters for the construction of linear chiral N,O-ketals

N,O-acetals are part of many synthetic intermediates and important skeletons of numerous natural products and pharmaceutical drugs. The most straightforward method of the synthesis of N,O-acetals is the enantioselective addition of O-nucleophiles to imines. However, using this method for the synthesis of linear chiral N,O-ketals still remains challenging due to the instability of raw materials under acidic or basic conditions. Herein, we developed a Cu-catalyzed asymmetric addition of alcohols to β,γ-alkynyl-α-imino esters under mild conditions, providing the corresponding linear chiral N,O-ketals with up to 96% ee. The method tolerates some variation in the β,γ-alkynyl-α-imino ester and alcohol scope, including some glucose and natural amino acid derivatives. Computational results indicate that the Boc group of the substrates assist in the extraction of hydrogen atoms from the alcohols to promote the addition reactions. These products could be synthesized on a gram-scale and can be used in several transformations. This asymmetric addition system provides an efficient, mild, gram-scale, and transition-metal-catalyzed synthesis of linear chiral N,O-ketals.

N,O-acetals are part of many synthetic intermediates and important skeletons of numerous natural products and pharmaceutical drugs. Here the authors show a Cu-catalyzed asymmetric addition of alcohols to β,γ-alkynyl-α-imino esters, providing the corresponding linear chiral N,O-ketals with up to 96% ee.

Electrochemical tandem trifluoromethylation of allylamines/formal (3 + 2)-cycloaddition for the rapid access to CF3-containing imidazolines and oxazolidines

A straightforward and environmentally friendly synthesis of CF₃-containing imidazolines and oxazolidines has been developed through an electrochemical three-component reaction among allylamines, the Langlois reagent, and nitrile or carbonyl compounds.

Stereoselective Syntheses of Highly Functionalized Imidazolidines and Oxazolidines via Ring-Opening Cyclization of Activated Aziridines and Epoxides with Amines and Aldehydes

A mild one-pot stereospecific synthetic route to highly functionalized imidazolidines and oxazolidines via S_N2-type ring-opening of the corresponding activated aziridines and epoxides with amines followed by p-toluenesulfonic acid (PTSA)-catalyzed intramolecular cyclization with aldehydes has been developed. The methodology tolerates a variety of functional groups and furnishes the desired products in high yields (up to 92%) with excellent stereoselectivities (de, ee > 99%). Interestingly, imidazolidines were formed as the cis-isomers, whereas oxazolidines were produced as trans-isomers exclusively.

Divergent synthesis of oxazolidines and morpholines via PhI(OAc)2-mediated difunctionalization of alkenes

Herein we describe the PhI(OAc)₂-mediated 1,1- and 1,2-difunctionalization of alkenes with N-tosyl amino alcohols to form oxazolidine and morpholine derivatives.

Organocatalytic synthesis of chiral CF3-containing oxazolidines and 1,2-amino alcohols: asymmetric oxa-1,3-dipolar cycloaddition of trifluoroethylamine-derived azomethine ylides

A series of CF₃-containing oxazolidines were constructed via organocatalytic asymmetric oxa-1,3-dipolar cycloaddition. These oxazolidines could undergo facile conversion to CF₃-containing 1,2-amino alcohols with vicinal stereogenic centers.

Cyclization Reaction of Donor-Acceptor Oxiranes with N,N'-Disubstituted Thioureas: A Domino Process to trans-Dihydropyrimidines

An unprecedented cyclization reaction of donor-acceptor oxiranes with N,N'-disubstituted thioureas to construct trans-dihydropyrimidines is presented. Preliminary reaction mechanism studies demonstrated that the reaction underwent sequential cycloaddition/amine ester exchange/oxygen-sulfur exchange/desulfuration/Michael addition process. A wide range of trans-dihydropyrimidines were produced with high yields up to 94% by using this method.

Organo-Catalyzed Regio- and Geometry-Specific Construction of β-Hydroxyl-α-vinyl Carboxylic Esters: Substrate Scope, Mechanistic Insights, and Applications

A green protocol has been developed for the synthesis of β-hydroxyl-α-vinyl carboxylic esters using aldehydes and α,β-unsaturated esters bearing an activated γ proton as starting materials under Morita-Baylis-Hillman (MBH) reaction conditions. Diverse β-hydroxyl-α-vinyl carboxylic esters have been synthesized regiospecifically in moderate to good yields with only E geometric selectivity. Other remarkable features include atom efficiency, environmental benignancy, and mild reaction conditions. Furthermore, the reaction products could be readily converted into tetrahydrofuran, dihydrofuran, and furan derivatives.

Expedient stereospecific Co-catalyzed tandem C–N and C–O bond formation of N-methylanilines with styrene oxides

The Co(ii)-catalyzed stereospecific sequential C–N and C–O bond formation of styrene oxides with N-methylanilines has been developed. Optically active epoxides can be coupled with high enantiomeric purity.

Unprecedented formation of 3-(tetrahydrofuran-2-yl)-4H-chromen-4-one in a reaction between 3,3a-dihydro-9H-furo[3,4-b]chromen-9-one and malononitrile

Chromone skeletons are widespread among natural products as well as bioactive molecules. Here, we describe an unprecedented reaction of furo[3,4-b]chromen-9-one with malononitrile to afford 3-(tetrahydrofuran-2-yl)-4H-chromen-4-ones. Experimental data suggest that a sequence of Michael/retro-Michael/nucleophilic addition is involved in this unprecedented transformation.