Cycloaddition Of Nitrile Oxides Research Articles

A novel protocol for the facile construction of tetrahydroquinoline fused tricyclic frameworks via an intramolecular 1,3-dipolar nitrile oxide cycloaddition reaction.

An efficient method towards the synthesis of quinoline fused tricyclic compounds involving an intramolecular 1,3-dipolar nitrile oxide cycloaddition reaction utilizing Baylis-Hillman derivatives in good yields has been described for the first time. A highly functionalized tricyclic framework was created by forming two rings and two adjacent stereocentres through the formation of two N-C bonds, one C-C bond and one O-C bond in a highly regio and diastereoselective manner.

Magnesium-Coordinated Chelation Control in 1,3-Dipolar Cycloaddition of Chiral α-Alkoxymethyl Ether Nitrile Oxide: Application to the Synthesis of (–)/(–)-cis-Clausenamide

A facile regio- and diastereoselective nitrile oxide cycloaddition method using magnesium-coordinated chelation control of chiral α-alkoxymethyl ether nitrile oxide is reported. This reaction could be successfully applied as a key step in both the formal total synthesis of (–)-clausenamide and the total synthesis of (–)-<i>cis</i>-clausenamide.

5-Substituted pyridylisoxazoles as effective inhibitors of platelet aggregation

A series of 5-substituted 3-pyridylisoxazoles were synthesized using [3+2] cycloaddition of nitrile oxides to alkynes with variation of substituents at position 5 of the isoxazole ring without additional synthetic stages and with retention of 2-pyridyl-, 3-pyridyl, and 4-pyridyl substituents at position 3 of the isoxazole ring. Substituted pyridylisoxazoles are the potential antiaggregatory agents showing in vitro activity in the concentration range from 1•10−6 mol L−1 to 1•10−4 mol L−1 toward the human platelet rich blood plasma with arachidonic acid being used as the inductor of aggregation. These compounds do not act as cyclooxygenase or thromboxane synthase inhibitors, nor as thrombin inhibitors.

ChemInform Abstract: An Environmentally Benign Synthesis of Isoxazolines and Isoxazoles Mediated by Potassium Chloride in Water.

Abstract1,3‐Dipolar cycloaddition of nitrile oxides, generated in situ by treatment of aldoximes with KCl and oxone in water, with alkenes or alkynes yields isoxazolines and isoxazoles, respectively.

Rapid Metal -free Macromolecular Coupling via in situ Nitrile Oxide-Activated Alkene Cycloaddition.

Nitrile oxide 1,3 dipolar cycloaddition is a simple and powerful coupling methodology. However, the self-dimerization of nitrile oxides has prevented the widespread use of this strategy for macromolecular coupling. By combining an in situ nitrile oxide generation with a highly reactive activated dipolarophile, we have overcome these obstacles and present a metal-free macromolecular coupling strategy for the modular synthesis of several ABA triblock copolymers. Nitrile oxides were generated in situ from chloroxime terminated poly(dimethylsiloxane) B-blocks and coupled with several distinct hydrophilic (poly(2-methyloxazoline) and poly(ethylene glycol)), and poly(N-isopropylacrylamide) or hydrophobic (poly(L-lactide) A-blocks terminated in activated dipolarophiles in a rapid fashion with high yield. This methodology overcomes many drawbacks of previously reported metal-free methods due to its rapid kinetics, versatility, scalability, and ease of introduction of necessary functionality. Nitrile oxide cycloaddition should find use as an attractive macromolecular coupling strategy for the synthesis of biocompatible polymeric nanostructures.

ChemInform Abstract: Stereoselective Synthesis of the CDE Ring System of Antitumor Saponin Scillascilloside E‐1.

AbstractThe tricyclic ring portion (I) of the eucosterol oligoglycoside scillascilloside E‐1 is synthesized via an Ireland—Claisen rearrangement and an intramolecular nitrile oxide cycloaddition.

Asymmetric synthesis of spiro[isoxazolin-3,3'-oxindoles] via the catalytic 1,3-dipolar cycloaddition reaction of nitrile oxides.

A highly enantioselective 1,3-dipolar cycloaddition of nitrile oxides with 3-arylidene-oxindoles was realized by a chiral N,N'-dioxide-nickel(II) complex catalyst under mild reaction conditions. A series of spiro-isoxazoline-oxindole derivatives were obtained in moderate yields (up to 65%) with good regioselectivities (up to 99:1), excellent enantioselectivities (up to 99% ee), and exclusive diastereoselectivity as well.

Azide based routes to tetrazolo and oxadiazolo derivatives of pyrrolobenzodiazepines and pyrrolobenzothiadiazepines

Tetrazolo- and 1,2,4-oxadiazolo-fused derivatives of the antitumour, antibiotic, DNA-interactive pyrrolo[2,1-c][1,4]benzodiazepines and their pyrrolobenzothiadiazepine derivatives have been produced as analogues of a 1,2,3-triazolo-fused pyrrolobenzothiadiazepine, which was shown to be a Glut-1 transporter inhibitor with potential as an antitumour agent. The tetrazolo-fused systems were produced by intramolecular 1,3-dipolar cycloaddition between an azide and a nitrile. The 1,2,4-oxadiazolo systems were produced by nitrile oxide cycloadditions to pyrrolobenzothiadiazepines, which were in turn produced from a 2-(azidobenzenesulfonyl)-1,2-thiazine 1-oxide. The latter species underwent a phosphite-mediated one-pot sulfur-extrusion, ring-contraction and azide to amine conversion to form 1-(aminobenzenesulfonyl)pyrroles. Bischler–Napieralski ring closure gave the pyrrolobenzothiadiazepines.

ChemInform Abstract: Chemoenzymatic Formal Total Synthesis of ent‐Codeine and Other Morphinans via Nitrone Cycloadditions and/or Radical Cyclizations. Comparison of Strategies for Control of C‐9/C‐14 Stereogenic Centers.

Formal total syntheses of ent-codeine and other morphinans were accomplished from 1-phenyl-2-acetoxyethane, which was subjected to enzymatic dihydroxylation by toluene dioxygenase overexpressed in Eschericia coli JM109 (pDTG601A). The resulting cis-dihydroarenediol was coupled with a phenol derived from bromoisovanillin and a subsequent Heck reaction was used to establish the C-13 quaternary center. Two strategies were employed to set the C-14 center: nitrone and nitrile oxide cycloadditions to the C-8/C-14 olefin and a radical cyclization of an aldehyde to C-14. Both strategies yielded tetracyclic products that were converted to known intermediates for the synthesis of ent-codeine, ent-codeinone, and ent-hydrocodone. Experimental and spectral data are provided for all new compounds.

ChemInform Abstract: Synthesis of 3,4‐Dibenzyltetrahydrofuran Lignans (9,9′‐Epoxylignanes)

AbstractReview: 51 refs.

Regio- and stereoselective access to novel ring-condensed steroidal isoxazolines

Novel 5α-androstanes containing an isoxazoline moiety condensed to ring A or D were efficiently synthetized by 1,3-dipolar cycloadditions of aryl nitrile oxides to steroidal α,β-unsaturated ketones. During the ring closures, regioisomers in which the O terminus of the nitrile oxide dipoles is attached to the β-carbon of the dipolarophile were formed in a stereoselective manner to furnish exclusively 1α,2α- or 15β,16β-condensed heterocycles. The cyclic enone moiety of the six-membered ring A proved to be less reactive than that of the five-membered ring D, but all the reactions were affected significantly by the substitution pattern of the nitrile oxide. 17-Deacetylation of the primary products resulted in aromatization or simultaneous hydroxylation, depending on the base applied for the ring A-fused heterocycles, while retro-Dieckmann-like fragmentation was observed partially or completely for the ring D-fused analogues during 3-deacetylation.

Design and synthesis of D-ring steroidal isoxazolines and oxazolines as potential antiproliferative agents against LNCaP, PC-3 and DU-145 cells

Two series of novel steroidal isoxazolines and oxazolines were synthesized through different routes from dehydroepiandrosterone acetate and pregnenolone acetate, respectively. The synthesis of the analogs of both series is multistep and proceeds in good overall yields. While the key step in the synthesis of former is the cycloaddition of aromatic nitrile oxides across α,β-unsaturated olefins, it is the condensation of α,β-azidoalcohols with aromatic aldehydes in the later. Compounds of both the series were tested for their cytotoxic activities against LNCaP, PC-3 and DU-145 prostate cancer cell lines. Amongst all the compounds of both the series screened for their prostate cancer activity, compound 6a, 6e and 12a are the most active especially against LNCaP and DU-145 cancer cell lines.

ChemInform Abstract: Hypervalent Iodine‐Catalyzed Cycloaddition of Nitrile Oxides to Alkenes

Abstractas a new and convenient procedure for the synthesis of isoxazolines

Synthesis of C-xylopyranosyl- and xylopyranosylidene-spiro-heterocycles as potential inhibitors of glycogen phosphorylase

New derivatives of d-xylose with aglycons of the most efficient glucose derived inhibitors of glycogen phosphorylase were synthesized to explore the specificity of the enzyme towards the structure of the sugar part of the molecules. Thus, 2-(β-d-xylopyranosyl)benzimidazole and 3-substituted-5-(β-d-xylopyranosyl)-1,2,4-triazoles were obtained in multistep procedures from O-perbenzoylated β-d-xylopyranosyl cyanide. Cycloadditions of nitrile-oxides and O-peracetylated exo-xylal obtained from the corresponding β-d-xylopyranosyl cyanide furnished xylopyranosylidene-spiro-isoxazoline derivatives. Oxidative ring closure of O-peracetylated β-d-xylopyranosyl-thiohydroximates prepared from 1-thio-β-d-xylopyranose and nitrile-oxides gave xylopyranosylidene-spiro-oxathiazoles. The fully deprotected test compounds were assayed against rabbit muscle glycogen phosphorylase b to show moderate inhibition for 3-(2-naphthyl)-5-(β-d-xylopyranosyl)-1,2,4-triazole (IC50=0.9mM) only.

Synthesis of Amido‐linked Oxazolyl/Thiazolyl/Imidazolyl Pyrazoles and Isoxazoles

The amido‐linked oxazolyl/thiazolyl/imidazolyl pyrazoles and isoxazoles were prepared from the synthetic intermediates oxazolyl/thiazolyl/imidazolyl acrylamides adpoting1,3‐dipolar cycloaddition of nitrile imines and nitrile oxides.

Investigations on intramolecular 1,3-dipolar cycloadditions for the synthesis of isoxazolo-annulated pyrrolidines, piperidines and azepanes

Pyrrolidines, piperidines, and azepanes with annulated isoxazole, isoxazoline or isoxazolidine rings were prepared by intramolecular 1,3-dipolar cycloadditions of nitrones or nitrile oxides. The corresponding 1,3-dipoles were obtained from N-Boc-protected and N-allyl-, N-propargyl- or N-(3-butenyl)-substituted 2-aminoethanal or 3-aminopropanal.

Synthesis of novel steroidal 16-spiroisoxazolines by 1,3-dipolar cycloaddition, and an evaluation of their antiproliferative activities in vitro

Efficient synthesis of novel 16-spiroisoxazolines in the androst-5-ene series was carried out by 1,3-dipolar cycloadditions of different aryl nitrile oxides to 3β-acetoxy-16-methylene-androst-5-en-17-one. During the intermolecular ring closures, the attack of the O terminus of the nitrile oxide dipole from the α side on C-16 predominated for steric reasons permitting the reactions to occur in a regio- and stereoselective manner. The minor isomers in which the angular methyl group on C-13 and the O atom of the isoxazoline heteroring were in the β, β-cis orientation were obtained in a yield of only ~10 %. Moreover, the conversions were influenced to a certain extent by the substituents on the aromatic moiety of the 1,3-dipoles. The stereostructures of the related diastereomers were confirmed by 2D NMR methods. Deacetylation of the primarily formed main products resulted in the corresponding 3β-OH analogs, which were further reduced to furnish 3β, 17β-diols. All of the synthetized compounds were subjected to in vitro pharmacological studies in order to investigate their antiproliferative effects on three malignant human adherent cell lines (HeLa, MCF7, and A431).

Stereoselective Synthesis of the CDE Ring System of Antitumor Saponin Scillascilloside E-1

A stereoselective synthesis of the CDE ring portion of the antitumor saponin scillascilloside E-1 has been achieved, utilizing an Ireland-Claisen rearrangement to construct the contiguous tetrasubstituted stereocenters at C13 and C17 simultaneously and intramolecular nitrile oxide cycloaddition to form the five-membered ring as key steps.

An environmentally benign synthesis of isoxazolines and isoxazoles mediated by potassium chloride in water

An effective and environmentally benign procedure for the synthesis of isoxazolines and isoxazoles has been developed by a cycloaddition of nitrile oxides with alkenes or alkynes in water. In this approach, potassium chloride is first oxidized into chlorine in water by the environmentally friendly oxidant Oxone®, then aldoximes are oxidized into nitrile oxides by the in situ generated hypochlorous acid, finally a 1,3-dipolar cycloaddition between nitrile oxides and alkenes or alkynes occurs to provide the corresponding isoxazolines and isoxazoles in good yields.

Chemoenzymatic Formal Total Synthesis of ent‐Codeine and Other Morphinans via Nitrone Cycloadditions and/or Radical Cyclizations. Comparison of Strategies for Control of C‐9/C‐14 Stereogenic Centers

AbstractFormal total syntheses of ent‐codeine and other morphinans were accomplished from 1‐phenyl‐2‐acetoxyethane, which was subjected to enzymatic dihydroxylation by toluene dioxygenase overexpressed in Eschericia coli JM109 (pDTG601A). The resulting cis‐dihydroarenediol was coupled with a phenol derived from bromoisovanillin and a subsequent Heck reaction was used to establish the C‐13 quaternary center. Two strategies were employed to set the C‐14 center: nitrone and nitrile oxide cycloadditions to the C‐8/C‐14 olefin and a radical cyclization of an aldehyde to C‐14. Both strategies yielded tetracyclic products that were converted to known intermediates for the synthesis of ent‐codeine, ent‐codeinone, and ent‐hydrocodone. Experimental and spectral data are provided for all new compounds.magnified image