Unexpected Ring Opening Research Articles

Unexpected ring opening of pyrazolines with activated alkynes: synthesis of 1H-pyrazole-4,5-dicarboxylates and chromenopyrazolecarboxylates.

1H-Pyrazole-4,5-dicarboxylates and chromenopyrazole carboxylates were prepared by reacting pyrazolines with activated alkynes under neat conditions without a catalyst. The products were formed via unexpected ring opening of pyrazolines with the elimination of styrene/ethylene. These types of transformations are unknown and the products formed were confirmed using their spectral/analytical data. In addition, the structures of compounds 5e and 5n were confirmed by single-crystal X-ray analysis. Control experiments were conducted to support the proposed reaction mechanism.

Unexpected ring-opening of 2,3-dihydropyridines

The reaction of 2,3-dihydropyridines with sulfonyl halides surprisingly yielded open chain dienes with sulfonylimine structure. The products were specific out of several possible isomers and, therefore, a separation of isomers was not necessary. All new compounds were characterized using FT-IR spectroscopy, HRMS, and NMR spectroscopy. A bicyclic by-product from the reaction of a 2,3-dihydropyridine with mesyl chloride was isolated and its structure elucidated using a single X-ray crystal analysis. Some biological activities, like antimicrobial and cytotoxic properties were investigated.Graphic abstract

Unexpected Ring Opening During the Imination of Camphor‐Type Bicyclic Ketones

AbstractA new ring opening reaction was found while attempting to isolate the imines from ortho‐heteroatom substituted anilines and camphor‐like bicyclic ketones. The benzoazoles containing a cyclopentanemethyl group at position 2 of the heterocycle were isolated instead of the expected imines. The detailed study of the transformation, including EPR experiments, revealed the most probable radical mechanism. The proposed reaction pathways were confirmed by quantum chemical calculations. The dichotomy of 1–2 and 2–3 bonds cleavage is discussed together with the evaluation of the stereochemical outcome of the reactions. The benzoazoles obtained via the new reaction are of particular interest for the medicinal chemistry.

Fulleropillar[4]arene: The Synthesis and Complexation Properties.

A multihydroquinone ether dialdehyde derivative 2 was incidentally obtained through an unexpected ring opening of pillar[4]arene[1]quinone 1. And the Prato reaction of 2 with [60]fullerene led to [60]fullerene bisadducts, from which trans-4 cyclic regioisomer 3 was isolated and characterized. The fulleropillar[4]arene 3 showed a larger cavity and can accommodate a viologen derivative C12V2+ with a much stronger affinity than permethyl pillar[5]arene (MP5) and pillar[4]arene[1]quinone 1.

Unexpected Oxidative Ring Opening of Electron-Rich 3-Aminobenzofurans into α-Ketoimines Derivatives

An unexpected ring opening of 3-aminobenzofurans promoted by NaO tBu in hot toluene, leading to a variety of α-ketoimines, is described. In the presence of 3-iodobenzofurans, NaO tBu mediates the 3-aminobenzofurans ring opening via a possible radical pathway without the help of any external radical sources.

Solvent-Free Ring Cleavage Hydrazinolysis of Certain Biginelli Pyrimidines

Certain Biginelli pyrimidines with ester substitution in C5 were subjected to unexpected ring opening upon solvent-free reaction with hydrazine hydrate to give three products: pyrazole, arylidenehydrazines, and urea/thiourea, respectively. The nonisolable carbohydrazide intermediates are formed firstly followed by the intermolecular nucleophilic attack of terminal amino group of hydrazide function on sp2 C6 rather than the sp3 C4 to give the ring adduct which was produced as a final product.

Synthesis of chiral 4,5-dihydrothiazol-2-amines and 4,5-dihydrooxazol-2-amines through an unexpected ring opening reaction of azetidines

A general and concise new method to the synthesis of chiral 4,5-dihydrothiazol-2-amines and 4,5-dihydrooxazol-2-amines has been developed. Chiral 4,5-dihydrothiazol-2-amines were made from the reaction of chiral 3-amino-4-aryl-azetidines with isothiocyanates via a completely regio- and stereoselective ring opening reaction of azetidines. And chiral 4,5-dihydrooxazol-2-amines were synthesized by the isomerization of the urea intermediates in the presence of TFA.

Lewis acid catalyzed [2+2] cycloaddition of ynamides and propargyl silyl ethers: synthesis of alkylidenecyclobutenones and their reactivity in ring-opening and ring expansion.

A family of four-membered enones, polysubstituted alkylidenecyclobutenones, were easily prepared by a Lewis acid catalyzed [2+2] cycloaddition of ynamides and propargyl silyl ethers. This challenging regioselective [2+2] cycloaddition enables the efficient construction and conversion of four-membered enones, which provides high-value and structurally diverse products through the unexpected ring-opening and ring expansion of alkylidenecyclobutenone with Grignard reagents, organolithium, primary amines, and water.

Synthesis of d-fructopyranosides with 2-O-acyl-β-d-fructopyranosides

Glycosylation of 2-O-acyl fructopyranosides was investigated, which were shown to be effective glycosyl donors for d-fructopyranoside synthesis with good β-selectivity and yields. For bulky acceptor 4e, α-anomer 5e was obtained with α/β=65:23. Unexpected ring-opening was observed during acetylation of 9, indicating the sensitivity of the fructopyranosyl ring.

Unexpected ring-opening of 3-aroylbenzo[b]furans at room temperature: a new route for the construction of phenol-substituted pyrazoles

Abstract A new and convenient route for the synthesis of phenol-substituted pyrazoles 11–18 is starting from 3-aroylbenzo[b]furans 1–8 and hydrazine hydrate at room temperature.

ChemInform Abstract: Ring Cleavage of Dihydropyrimidine Skeleton.

AbstractNucleophilic reaction of substrate (I) with anilines and phenylhydrazine results in unexpected ring opening to yield compounds of type (III).

Formation of stable iron/cobalt NHC complexes via unexpected ring opening and in situ generation of a tridentate ligand

The reactions of FeCl(2) and CoCl(2) with a bistriazolium salt yields the NHC complexes [Fe(III)(L1)(2)]I·H(2)O, [Fe(III)(L2)(2)]PF(6)·CH(3)CN and [Co(III)(L1)(2)]I·0.5CH(3)CN, through an unusual ring opening of one of the triazoyl rings, which leads to the formation of C,N,O tridentate ligands L1 or L2. Furthermore, a Fe(ii) species [Fe(II)(L1)(2)]·CH(2)Cl(2) was also obtained.

Synthesis of functionalized 2,3-dihydroisoxazoles by domino reactions in water and unexpected ring-opening reactions of 2,3-dihydroisoxazoles

α,α-Dicyanoolefins react with hydroxylamine to afford 2,3-dihydroisoxazoles (2,3-dihydroisoxazoles can be easily isolated by filtration) in excellent yields under mild and environmentally benign conditions. A one-pot reaction in tandem with an unexpected ring-opening of 2,3-dihydroisoxazoles has been developed as well.

Synthesis and immunostimulatory activity of diethanolamine-containing lipid A mimics

Toll-like receptor (TLR) 4 plays important roles in the innate immunity and the development of adaptive immune responses. TLR4 ligands that can modulate the TLR4-mediated signalling pathways therefore have great potential for therapeutic applications. In this paper, we describe the synthesis of three lipid A mimics (2–4) as potential TLR4 ligands, in which a diethanolamine moiety is employed to replace the reducing end (D-glucosamine) of the archetypical lipid A disaccharide structure. Biological studies indicate that the lipid A mimic with six acyl chains (2) exhibits potent immune stimulatory activity in that it induces a significant increase in the ICAM-1 expression of human pre-monocytic THP-1 cells, as well as significant production of the cytokines TNF-α, IL-6, and IL-1β. The mimic with eight acyl chains (3) is inactive towards both the induction of ICAM-1 expression, and the cytokines TNF-α, and IL-6, yet induces significant production of IL-1β when tested at higher concentration. Finally, the lipid A mimic 4, a derivative of 2, that contains an additional 1-hydroxybutyl group as a result of an unexpected ring opening reaction of a tetrahydrofuran molecule, is active in all respects tested, albeit with reduced potency. These data suggest that diethanolamine-containing lipid A mimics can be potent immune stimulating agents.

ChemInform Abstract: Efficient Iminophosphorane‐Mediated Preparation of Benzofuro[3,2‐d]pyrimidine‐4(3H)‐ones and Unexpected Ring Opening Products.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Efficient Iminophosphorane‐Mediated Preparation of Benzofuro[3,2‐d]pyrimidin‐4(3H)‐ones and Unexpected Ring Opening Products

AbstractThe carbodiimides 4, obtained from aza‐Wittig reactions of iminophosphorane 3 with aromatic isocyanates, reacted with secondary amines, phenols or alcohols in the presence of catalytic amounts of K2CO3 or sodium alkoxide to give 2‐substituted benzofuro[3,2‐d]pyrimidin‐4(3H)‐ones 6. However, when 2,2′‐iminobis[ethanol] was used, the unexpected ring opening product 7 was formed instead of 6. Reaction of 4 with primary amines RNH2 (R=Et, Pr, Bu, etc.) gave guanidine intermediates 8, which were further treated with EtONa to give only one regioisomer 9 via a base catalyzed cyclization. However, another regioisomer 11 was obtained when NH3 or ‘small’ amines RNH2 (R=Me, NH2) were used in the absence of EtONa via a spontaneous cyclization of 8.

Unexpected Ring-opening Reaction of Aziridine with Acetic Anhydride in DMF

Abstract Ring-opening reactions of aziridines with acetic anhydride in DMF afforded the unexpected β-amino formate in moderate to good yields. The possible mechanism is also proposed.

Unexpected Ring‐Opening of a 2‐Pyrone Ring in the Synthesis of 3‐[(Z)‐1‐Hydroxy‐3‐oxobut‐1‐enyl]‐2H‐chromen‐2‐one Derivatives (III) Catalyzed by KF‐Alumina.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF.

Unexpected Ring-Opening of a 2-Pyrone Ring in the Synthesis of 3-[(Z)-1-Hydroxy-3-Oxobut-1-Enyl]-2H-chromen-2-One Derivatives Catalysed by Kf-Alumina

A series of 3-[( Z)-1-hydroxy-3-oxobutenyl]-2 H-chromen-2-one derivatives were synthesised by an unexpected ring-opening of a 2-pyrone ring reaction of substituted salicylaldehydes, and 4-hydroxy-6-methyl-pyran-2-one in ethyl alcohol at room temperature catalysed by KF-Al2O3. The enol structure of the product not ketone was characterised by 1H NMR, IR and elemental analysis, and enol and ( Z)-structure further confirmed by X-ray diffraction analysis.

Unexpected Ring-Opening Reactions of Aziridines with Aldehydes Catalyzed by Nucleophilic Carbenes under Aerobic Conditions

[reaction: see text] The chemoselective ring opening of N-tosyl aziridines with aldehydes catalyzed by an N-heterocyclic carbene was investigated under aerobic conditions. Unexpected carboxylates of 1,2-amino alcohols from the corresponding aldehydes, rather than the acyl anion ring-opened beta-amino ketones, were exclusively obtained. A plausible mechanism for this unprecedented carbene-mediated reaction was also proposed.