Thermal cycloaddition of carbonyl compounds to a stable cyclobutadiene

In contrast to acid chlorides which undergo addition to 1 to form cyclobutene derivatives 4, aldehydes react with the same antiaromatic starting compound 1 to give the [4+2]-cycloaddition product 5. Activated ketones such as 1,1,1-trifluoroacetone, biacetyl, and acetyl cyanide undergo a clean cycloaddition reaction to tricyclic compounds (1 + 6a?c → 9a?c), whereas trioxoindane yields a bicyclic product (1 + 6d → 8d).     

Catalytic asymmetric synthesis of stable oxetenes via Lewis acid-promoted [2+2] cycloaddition

A highly enantioselective and atom-economical [2 + 2] cycloaddition of various alkynes with trifluoropyruvate using a dicationic (S)-BINAP-Pd catalyst has been established. This is the first enantioselective synthesis of stable oxetene derivatives, whose structure has been clarified by X-ray analysis. This catalytic process offers a practical synthetic method for oxetene derivatives (catalyst loading: up to 0.1 mol %), which can serve as novel chiral building blocks for pharmaceuticals and agrochemicals and can also be transformed into a variety of enantiomerically enriched CF(3)-substituted compounds with high stereoselectivity.     

Asymmetric polymerization via cycloaddition reactions

The reaction of N‐phthaloyl‐L ‐leucine acid chloride (1) with isoeugenol (2) was carried out in chloroform, and novel optically active isoeugenol ester derivative 3 as a chiral monomer was obtained in high yield. Compound 3 was characterized by ¹H‐NMR, IR, and mass and elemental analysis and then was used for the preparation of model compound 5 and polymerization reactions. 4‐Phenyl‐1,2,4‐triazoline‐3,5‐dione, PhTD (4), was allowed to react with compound 3. The reaction is very fast and gives only one diastereomer of 5 via Diels–Alder and ene pathways in quantitative yield. In order to explain this diastereoselectivity, a nonconcerted two‐step mechanism involving benzylic cation (BC) and aziridinium (AI) have been proposed for the Diels–Alder and ene reactions, respectively. The polymerization reactions of novel monomer 3 with bis(triazolinedione)s [bis(p‐3,5‐dioxo‐1,2,4‐triazolin‐4‐ylphenyl)methane (8) and 1,6‐bis(3,5‐dioxo‐1,2,4‐triazolin‐4‐yl)hexane] (9)] were performed in N,N‐dimethylacetamide (DMAc) at room temperature. The reactions are exothermic, fast, and gave novel optically active polymers 10 and 11 via repetitive Diels–Alder–ene polyaddition reactions. These polymers have inherent viscosities in a range about 0.18–0.22 dL/g. Some physical properties and structural characterizations of these new polymers have been studied and are reported. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 1211–1219, 1999     

Synthesis of fullerene glycoconjugates via a copper-catalyzed Huisgen cycloaddition reaction

The synthesis of fullerene-carbohydrate conjugates using a copper-catalyzed [3+2] cycloaddition reaction to facilitate the union of an azido-functionalized sugar and a pentaalkynyl[60]fullerene is straightforward. Thus, fullerenes bearing five oligosaccharides such as Gb3-trisaccharide can be readily accessed. Nanometer-scale molecular architectures presenting as many as 15 sugar moieties in C5-symmetry are readily produced. The cycloaddition reaction proceeds quantitatively under mild conditions without the need to protect the sugar hydroxyl groups.     

The preparation of intercalating isoxazoles via a nitrile oxide cycloaddition

Pyridinium chlorochromate oxidation of 9-methylacridine (2) affords the corresponding aldehyde 3 in good yield. Conversion of the aldehyde to the hydroximinoyl chloride 5a was accomplished via reaction of the corresponding oxime with N-chlorosuccinimide. Dipolar addition to the enamine of ethylacetoacetate provided the corresponding isoxazoles 1 in good yield.     

Formation and cycloaddition reactions of ferrocenyl nitrones

Ferrocenyl nitrones derived from aldehydes or oximes react with electron deficient alkenes to give ferrocenylisoxazolidines. 5‐Methoxycarbonylisoxazolidines are further transformed to ferrocenyl‐pyrrolidinones by reductive cleavage. The regio‐ and stereoselectivity of the reactions are discussed.     

Glycosyl transfer to nitrogen via cycloaddition

[formula: see text] This letter describes the reduction to practice of a novel concept for functionalization of the anomeric carbon of carbohydrates with a nitrogen substituent. Thus, bisheterodienes with a thiono sulfur terminus and a sulfonylimine terminus are shown to undergo cycloaddition smoothly and stereoselectively to three different glycals.     

Segment block dendrimers via Diels-Alder cycloaddition

Segment block dendrimers consisting of polyester and polyaryl ether dendrons were synthesized using reagent free Diels-Alder cycloaddition reactions. Three generations of furan functionalized polyaryl ether dendrons were reacted with maleimide functionalized polyester dendrons of the same generation to obtain segment block dendrimers in good yields. The thermoreversible nature of these macromolecules was investigated by subjecting them to elevated temperatures in the presence of anthracene as a scavenger diene.     

Enantiospecific synthesis of β-lactams via cycloaddition

Enantiospecific synthesis of variously substituted cis-β-lactams can be achieved by the annelation of Schiff bases from optically active ketal aldehydes derived from D-threonine. Similar annelation of Schiff bases from the triphenylsilyl ether of D-threonine ester and cinnamaldehyde leads to cis-β-lactams with high diastereofacial selectivity.     

Synthesis of celecoxib via 1,3-dipolar cycloaddition

A regioselective 1,3-dipolar cycloaddition reaction between a nitrile imine and an enamine is described for the preparation of celecoxib. Nitrile imines are generated in situ from the corresponding hydrazonoyl benzenesulfonates.     

A stable nitroxide - 2,2,5,5-tetramethyl-3-imidazoline-3-oxide-1-oxyl - a reagent for spin labeling via 1,3-dipolar cycloaddition

The paramagnetic heterocyclic aldonitrone, 2,2,5,5-tetra-methyl-3-imidazoline-3-oxide-1-oxyl, reacts with C=C and C=N containing dipolarophiles to yield cycloadducts with radical centres.     

New monomers and polymers via Diels-Alder cycloaddition

The series of new bis(naphthalic anhydrides) was prepared through Diels-Alder cycloaddition. The Diels-Alder cycloaddition was used as a synthetic route to new phenylated monomers as well as to polymers. All polymers synthesized revealed to be soluble in a wide range of organic solvents such as toluene, THF, chloroform, and displayed high thermostability. Therefore, they can be processed easily and are promising candidates for advanced coating systems as well as for electrooptical applications.     

Synthesis of stable ketenimines via a four-component reaction

Abstract  

An efficient one-pot synthesis of ketenimine derivatives is described. It involves a four-component reaction between benzylamines, 2,2-dichloroethanoyl chloride, alkyl isocyanide, and dialkyl acetylenedicarboxylates under mild conditions at ambient temperature.     

Synthesis of spirooxindoles via asymmetric 1,3-dipolar cycloaddition

An efficient method was developed for the asymmetric synthesis of 2′-alkyl-4′aryl-1H-spiro[indole-3,3′-pyrrolidin]-2-ones, which are potential inhibitors of the p53-MDM2 interaction. Our X-ray crystallographic analysis revealed that this 1,3-dipolar cycloaddition proceeds with high stereoselectivity but differently from previously published results.     

Total synthesis of (+/-)fasicularin via a 2-amidoacrolein cycloaddition

The total synthesis of the cytotoxin fasicularin is described. The key steps include the following: (1) an intermolecular Diels-Alder cycloaddition of a 2-(triflamido)acrolein with the dioxolane ketal of trideca-1,3-dien-7-one to establish the trans-perhydroisoquinoline stereochemistry, (2) a stereoelectronically controlled hydride addition to a N(1)-C(2) iminium ion to introduce the equatorial hexyl substituent, and (3) elaboration of the pyrido ring by an internal aldol reaction.     

Reagentless functionalization of gold nanoparticles via a 3 + 2 Huisgen cycloaddition

A mild method for functionalization of gold nanoparticles is reported. The reactions of azide functionalized nanoparticles with propynoic acid derivatives provide triazole functionalized nanoparticles under very mild reaction conditions. Characterization of the nanoparticle-bound triazoles using (1)H and (13)C NMR spectroscopy indicates that both the 1,4 and 1,5 triazole regioisomers are formed on the nanoparticle surface.     

The total synthesis of (±) kawain via a hetero-diels-alder cycloaddition

The hetero-Diels-Alder reaction between 1,3-dimethoxy-1-trimethylsilyloxybutadiene $\text{4}$, and cinnamaldehyde$\text{5}$, produces (±) kawain in 75% and 84% yield respectively when catalyzed by Eu(fod)₃ or Yb(fod)₃. When Ag(fod) is employed as the catalyst a unique condensation reaction occurs which produces two acyclic diastereomers in 72% yield.     

Isocyanurate anion radicals via electron-initiated cycloaddition of isocyanates

Room temperature sodium metal reductions of alkyl isocyanates lead to the rapid electron-initiated formation of alkyl isocyanurate anion radicals, which exhibit EPR coupling to only two equivalent nitrogens. Reduction of (13)C-enriched ethyl isocyanate reveals that the odd electron localizes in the pi system of one carbonyl in the isocyanurate ring. EPR line-width alternation effects indicate that at least two stable conformers are in rapid equilibrium undergoing fast exchange.