Tetrabutylammonium Iodide Catalyzed Synthesis of Allylic Ester with tert-Butyl Hydroperoxide as an Oxidant

Metal-Free Bisamidation of N-Tosylhydrazones with Carboxylic Acids Promoted by Tetrabutylammonium Iodide and tert-Butyl Hydroperoxide

A versatile reaction between N-tosylhydrazones and carboxylic acids to access bisamides is reported. This metal-free, room-temperature reaction was catalyzed by TBAI, while TBHP served as the oxidant. Broad substrate scope and good functional group tolerance are the key features of the strategy. Subsequent intramolecular N-arylation of suitably substituted bisamides readily afforded functionalized 3-indazolones.

TBAI-Catalyzed Oxidative Coupling of Benzyl Ketones to Synthesize 2,3-Diaryl-1,4-Diketones in Water

An efficient and green route of C-C bond formation was disclosed to construct 2,3-diaryl-1,4-diketones from α-methylene ketones by the catalysis of tetrabutylammonium iodide (TBAI) with tert-butyl hydroperoxide (TBHP) as an oxidant in water. This reaction affords the desired products in good to excellent yields from readily available materials, with a broad substrate scope, good functional group tolerance, and mild reaction conditions. Furthermore, tetrasubstituted furan and pyrrole were smoothly constructed from α-methylene ketones in one pot with 96 and 90% yields, respectively.

Intermolecular CDC amination of remote and proximal unactivated Csp3 -H bonds through intrinsic substrate reactivity - expanding towards a traceless directing group

An intermolecular radical based distal selectivity in appended alkyl chains has been developed. The selectivity is maximum when the distal carbon is γ to the appended group and decreases by moving from γ → δ → ε positions. In –COO– linked alkyl chains, the same distal γ-selectivity is observed irrespective of its origin, either from the alkyl carboxy acid or alkyl alcohol. The appended groups include esters, N–H protected amines, phthaloyl, sulfone, sulfinimide, nitrile, phosphite, phosphate and borate esters. In borate esters, boron serves as a traceless directing group, which is hitherto unprecedented for any remote C_sp³–H functionalization. The selectivity order follows the trend: 3° benzylic > 2° benzylic > 3° tertiary > α to keto > distal methylene (γ > δ > ε). Computations predicted the radical stability (thermodynamic factors) and the kinetic barriers as the factors responsible for such trends. Remarkably, this strategy eludes any designer catalysts, and the selectivity is due to the intrinsic substrate reactivity.

An intermolecular amination at the distal methylene carbon has been realized in an appended alkyl chain with electron withdrawing groups. Traceless remote C_sp³–H functionalization has been accomplished using borate esters.

Synthesis of (+)-Panamonon B, 7-epi-Panamonon B, and Their (Z)-Isomers

(+)-Panamonon B was synthesized with the key quaternary center (of a predefined absolute configuration) installed using Stoltz asymmetric allylation. The C-5 ketone functionality and the cross-conjugated enone moiety in the side chain were introduced via a photosensitized [2+4] cycloaddition of singlet oxygen to diene silyl enol ether and an aldol condensation under the conditions of Sugiura, respectively. The ¹H and ¹³C NMR of the synthetic and natural samples were fully consistent with each other. However, because two samples showed opposite signs for optical rotations, they must be antipodes to one another. The synthesis also provided valuable chances to observe unexpected, yet rather intriguing, phenomena such as a bulky substituent in an axial position of a cyclohexane ring and (E)-and (Z)-isomers with opposite signs for optical rotations despite their identical stereogenic centers. The rare occurrence of a bulky substituent in an axial position of a cyclohexane ring is rationalized as a consequence of the presence of a quaternary center and formation of the five-membered lactone fused to the six-membered ring, while the so far unnoticed influence of C═C geometry on optical rotation is shown to be consistent with the information encapsulated in several discrete pairs of similar compounds retrieved from the literature.

A copper iodide-catalyzed coupling reaction of benzofuran-3(2H)-ones with amines: an approach to α-ketoamides

A CuI-catalyzed coupling reaction of benzofuran-3(2H)-ones with amines has been well established for the direct synthesis of α-ketoamides. This process involves C-O bond cleavage and C[double bond, length as m-dash]O/C-N bond formation. Mechanism studies indicated that this α-ketoamide formation reaction may involve a free radical process.

Metal-Free C-H Functionalization of Allenamides: An Access to Branched Allylic Esters

A regioselective acyloxylation with carboxylic acids at the proximal carbon of allenamides by an N-iodosuccinimide-mediated C-H functionalization is reported. The reaction proceeds rapidly, is scalable to a gram scale, and displays a broad substrate scope, providing an efficient and practical protocol for the synthesis of branched allylic esters. Notably, protected amino acids were tolerated under the reaction conditions and afforded allylic amino acid esters in moderate yields.

Iodine promoted dual oxidative C(sp3)-H amination of 2-methyl-3-arylquinazolin-4(3H)-ones: a facile route to 1,4-diarylimidazo[1,5-a]quinazolin-5(4H)-ones

An iodine promoted tandem oxidative condensation of benzylamines and 2-methylquinazolin-4-(3H)-ones was developed to yield imidazo[1,5-a]quinazolin-5(4H)-ones via dual C(sp³)-H amination under metal free conditions in a greener way using molecular oxygen as a terminal oxidant. This tandem transformation provides an efficient approach to construct various functionalized imidazo[1,5-a]quinazolin-5(4H)-ones in a straightforward manner via a sequential amination-oxidation-annulation-aromatisation.

C-H functionalisation of cycloalkanes

Among organic compounds hydrocarbons are inexpensive and possibly the most abundant among natural resources. Developing strategies for selective functionalisation of inert hydrocarbon C-H bonds is one of the most ideal synthetic paths that a synthetic chemist could think of. This critical review focuses on the recent development of various directed and non-directed cycloalkylations leading to the formation of carbon-carbon (C-C) and carbon-heteroatom (C-X) bonds. Apart from various transition metal catalysed cycloalkylations, this review also covers various metal-free cycloalkylation processes.

Directing activator-assisted regio- and oxidation state-selective aerobic oxidation of secondary C(sp(3))-H bonds in aliphatic alcohols

The regioselective conversion of an unactivated C(sp(3))-H bond of a methylene carbon (CH2) into a C-O single bond is an attractive reaction in organic synthesis. Herein, we present a strategy for a regio- and oxidation state-selective aerobic C-H oxidation based on an N-hydroxyamide-derived directing activator (DA), which is attached to a hydroxy group in alcohol substrates. The DA reacts with NOx species generated in situ from NaNO2, a Brønsted acid, and aerobic oxygen, and effectively generates an amidoxyl radical from the N-hydroxy moiety of the DA. Then, the amidoxyl radical promotes site-selective intramolecular C-H abstraction from methylenes with γ- (or δ-) selectivity. The thus-generated methylene radicals are trapped by molecular oxygen and NO. This process results in the predominant formation of nitrate esters as products, which suppresses undesired overoxidation. The products can be easily converted into alcohols after hydrogenolysis.

Synthetic access to isoxazoline-functionalized isoquinolines via microwave-assisted iminoxyl radical-participated cascade cyclization of vinyl isocyanides

The synthesis of isoxazoline-functionalized isoquinolines via radical cascade cyclization of vinyl isocyanides with β,γ-unsaturated ketoximes has been described.

Selectfluor-induced C(sp2)–O coupling reaction of N-substituted anilines with hydroxylamine derivatives

We developed a novel metal-free method for the construction of C(sp²)–O bonds via oxidative cross-coupling reactions between various N-substituted anilines and hydroxylamine derivatives just using commercially available Selectfluor as an oxidant.

A photoinduced cross-dehydrogenative-coupling (CDC) reaction between aldehydes and N-hydroxyimides by a TiO2–Co ascorbic acid nanohybrid under visible light irradiation

A TiO₂–Co ascorbic acid nanohybrid as an efficient photocatalyst catalyzed the selective synthesis of N-hydroxyimide esters through visible light irradiation.

Iodine-mediated synthesis of 4-selanylpyrazoles

A new and simple procedure mediated by I₂ is developed for the preparation of 4-selanylpyrazoles from pyrazoles and diselenides.