Iterative direct C(sp3)–H functionalization of amines: diastereoselective divergent syntheses of α,α′-disubstituted alicyclic amines

Facile access to the syn-α,α′-disubstituted N-heterocycles via iterative C–H oxygenation and C–C bond formation.

Oxidative C–H functionalization of N-carbamoyl 1,2-dihydroquinolines

A modular and efficient method for the synthesis of α-substituted 1,2-dihydroquinolines through an oxidative C–H functionalization strategy is described.

Recent progress in mild Csp3–H bond dehydrogenative or (mono-) oxidative functionalization

This review summarizes recent advances in mild and green dehydrogenative and mono-oxidative Csp³–H bond functionalization reactions, considering both new approaches and the re-elaboration of known methodologies.

Diastereoselectively Complementary C-H Functionalization Enables Access to Structurally and Stereochemically Diverse 2,6-Substituted Piperidines

The preparation of 2,6-substituted piperidine derivatives through diastereoselective C-H functionalization of corresponding nitrogen heterocycles represents an appealing protocol and yet remains a formidable challenge. Here, we describe a stereochemically complementary oxidative C-H functionalization of N-carbamoyl tetrahydropyridines with a wide variety of building blocks, providing either the cis- or trans-2,6-substituted piperidines with diverse patterns of functionalities. The mild metal-free process exhibits excellent regio- and diastereoselectivities as well as functional group tolerance. The synthetic utilities in natural product and analogue syntheses are also described.

Novel Benzo[a]quinolizidine Analogs Induce Cancer Cell Death through Paraptosis and Apoptosis

Paraptosis is nonapoptotic cell death characterized by massive endoplasmic reticulum (ER)- or mitochondria-derived vacuoles. Induction of paraptosis offers significant advantages for the treatment of chemotherapy-resistant tumors compared with anticancer drugs that rely on apoptosis. Because some natural alkaloids induce paraptotic cell death, a novel series of benzo[a]quinolizidine derivatives were synthesized, and their antiproliferative activity and ability to induce cytoplasmic vacuolation were analyzed. Structural optimization led to the identification of the potent compound 22b, which inhibited cancer cell proliferation in vitro and in vivo and profoundly facilitated paraptosis-like cell death and induced caspase-dependent apoptosis. Further investigation revealed that 22b-mediated vacuolation originated from persistent ER stress and upregulation of LC3B. Paraptosis induced by benzo[a]quinolizidine derivatives thus represents an alternative strategy for cancer chemotherapy.

Enolizable Carbonyls and N,O-Acetals: A Rational Approach for Room-Temperature Lewis Superacid-Catalyzed Direct α-Amidoalkylation of Ketones and Aldehydes

An efficient catalytic room-temperature direct α-amidoalkylation of carbonyl donors, that is, ketones and aldehydes with unbiased N,O-acetals, is described. Sn(NTf2 )4 is an optimal catalyst to promote this challenging transformation at low loading and the reaction shows promising scope. A comprehensive and rational evaluation of this reaction has led to the establishment of an empirical scale of nucleophilic reactivity for a broad set of ketones that should be helpful in the synthetic design and development of carbonyl α-functionalization methods.

Synthesis of α-sulfenyl monoketones via a metal-free oxidative cross dehydrogenative coupling (CDC) reaction

α-Sulfenyl ketones are potential precursors which find a variety of applications in organic synthesis.

A practical oxidative C–H functionalization of N-carbamoyl tetrahydro-β-carbolines with diverse potassium trifluoroborates

A practical and mild metal-free oxidative C–H functionalization ofN-carbamoyl tetrahydro-β-carbolines with diverse potassium trifluoroborates has been reported.

Versatile and highly efficient oxidative C(sp3)–H bond functionalization of tetrahydroisoquinoline promoted by bifunctional diethyl azodicarboxylate (DEAD): scope and mechanistic insights

The oxidant–base bifunctionality of DEAD realized highly reliable cross dehydrogenative coupling of tetrahydroisoquinoline derivatives via aminal intermediates.

Direct C-H Allylation of N-Acyl/Sulfonyl Tetrahydroisoquinolines and Analogues

A highly efficient direct C-H allylation reaction at the α position of N-acyl/sulfonyl tetrahydroisoquinolines under mild conditions was developed. The reaction was also suitable for allylation of other protected nitrogen-containing heterocycles. Several interesting transformations of the products into valuable synthetic intermediates are featured with the successful total synthesis of (±)-crispine A.

Metal-Free Oxidative C-C Bond Formation through C-H Bond Functionalization

The formation of C-C bonds embodies the core of organic chemistry because of its fundamental application in generation of molecular diversity and complexity. C-C bond-forming reactions are well-known challenges. To achieve this goal through direct functionalization of C-H bonds in both of the coupling partners represents the state-of-the-art in organic synthesis. Oxidative C-C bond formation obviates the need for prefunctionalization of both substrates. This Minireview is dedicated to the field of C-C bond-forming reactions through direct C-H bond functionalization under completely metal-free oxidative conditions. Selected important developments in this area have been summarized with representative examples and discussions on their reaction mechanisms.

Benzhydrylium and tritylium ions: complementary probes for examining ambident nucleophiles

The linear free energy relationship log k = sN(N + E) (eq. 1), in which E is an electrophilicity, N is a nucleophilicity, and sN is a nucleophile-dependent sensitivity parameter, is a reliable tool for predicting rate constants of bimolecular electrophile-nucleophile combinations. Nucleophilicity scales that are based on eq. (1) rely on a set of structurally similar benzhydrylium ions (Ar2CH+) as reference electrophiles. As steric effects are not explicitely considered, eq. (1) cannot unrestrictedly be employed for reactions of bulky substrates. Since, on the other hand, the reactions of tritylium ions (Ar3C+) with hydride donors, alcohols, and amines were found to follow eq. (1), tritylium ions turned out to be complementary tools for probing organic reactivity. Kinetics of the reactions of Ar3C+ with π-nucleophiles (olefins), n-nucleophiles (amines, alcohols, water), hydride donors and ambident nucleophiles, such as the anions of 5-substituted Meldrum’s acids, are discussed to analyze the applicability of tritylium ions as reference electrophiles.

Highly enantioselective catalytic cross-dehydrogenative coupling of N-carbamoyl tetrahydroisoquinolines and terminal alkynes

The first catalytic asymmetric cross-dehydrogenative coupling of cyclic carbamates and terminal alkynes has been established. The reaction features high enantiocontrol and excellent functional group tolerance and displays a wide range of structurally and electronically diverse carbamates as well as terminal alkynes. N-Acyl hemiaminals were identified as the reactive intermediates through preliminary control experiments. Employing readily removable carbamates as substrates rather than traditionally adopted N-aryl amines allows applications in complex molecule synthesis and therefore advances the C-H functionalization strategy to a synthetically useful level.

nBu4NI-catalyzed intermolecular C–O cross-coupling reactions: synthesis of alkyloxyamines

nBu₄NI-catalyzed cross-coupling of benzyl and allylic compounds with N-hydroxyphthalimide for the synthesis of alkyloxyamines were realized for the first time.

Indium-catalyzed oxidative cross-dehydrogenative coupling of chromenes with 1,3-dicarbonyls and aryl rings

An efficient indium-catalyzed oxidative cross-dehydrogenative coupling of chromenes with 1,3-dicarbonyls and aryl rings promoted by DDQ was described.

C1-Benzyl and benzoyl isoquinoline synthesis through direct oxidative cross-dehydrogenative coupling with methyl arenes

An oxidative cross-dehydrogenative coupling of isoquinolines with methyl arenes has been developed, yielding structurally diverse C₁-benzyl and -benzoyl isoquinolines selectively. The direct use of readily available methyl arenes as coupling partners avoids unproductive steps for preactivating functional group installation, and is thereby attractive.

Copper(ii)/amine synergistically catalyzed enantioselective alkylation of cyclic N-acyl hemiaminals with aldehydes

A copper/amine synergistic catalytic system was developed, allowing the first catalytic asymmetric alkylation of N-acyl quinoliniums with aldehydes in high yields and excellent enantioselectivities.

TBHP/TFA mediated oxidative cross-dehydrogenative coupling of N-heterocycles with aldehydes

A metal-free oxidative cross-dehydrogenative coupling of N-heterocycles with diverse aldehydes has been established in the presence of TBHP/TFA.

Structurally diverse α-substituted benzopyran synthesis through a practical metal-free C(sp3)-H functionalization

A trityl ion-mediated practical C-H functionalization of a variety of benzopyrans with a wide range of nucleophiles (organoboranes and C-H molecules) at ambient temperature has been disclosed. The metal-free reaction has an excellent functional group tolerance and high chemoselectivity and displays a broad scope with respect to both benzopyran and nucleophile partners, efficiently affording a collection of benzopyrans bearing diverse skeletons and α-functionalities in one step.

Practical and highly selective C-H functionalization of structurally diverse ethers

A trityl ion mediated C-H functionalization of ethers with a wide range of nucleophiles at ambient temperature has been developed. The reaction displays high chemoselectivity and good functional group tolerance. The protocol also exhibits excellent regio- and diastereoselectivities for the unsymmetric ethers, thus stereoselectively generating highly functionalized disubstituted 2,5-trans tetrahydrofurans (THF), 2,6-trans tetrahydropyrans (THP), 2,6-trans dihydropyrans (DHP), and 1,3-trans isochromans, and highlighting the capacity of the protocol in complex molecule synthesis.