Enantioselective 1,3‐dipolar cycloaddition reactions using complexes of (−)‐sparteine

Regio‐ and stereoselective 1,3‐dipolar cycloaddition of nitrile oxides to internal 2‐pentenols and α,β‐unsaturated esters catalyzed by (?) sparteine‐lanthanide complexes affords corresponding 3‐aryl‐2‐isoxazolines with enantioselectivities up to 68% ee.     

Nitropyridyl isocyanates in 1,3‐dipolar cycloaddition reactions

The reactivity of 3‐nitro‐4‐pyridyl isocyanate ( 7 ) and 5‐nitropyridin‐2‐yl isocyanate ( 9 ) in 1,3‐dipolar cycloaddition reactions with azides and pyridine N‐oxides has been investigated. 1,3‐Dipolar cycloaddition to trimethylsilylazide (TMSA) afforded the respective tetrazolinones, 1‐(3‐nitropyridin‐4‐yl)‐1H‐tetrazol‐5(4H)one ( 8 , 50 %) and 1‐(5‐nitropyridin‐2‐yl)‐1H‐tetrazol‐5(4H)one ( 11 , 64 %). Respectively, 1,3‐dipolar cycloaddition of nitropyridyl isocyanates 7 and 9 to 3,5‐dimethylpyridine N‐oxide ( 14 ), 3‐methylpyridine N‐oxide ( 21 ) and pyridine N‐oxide ( 22 ) gave the substituted amines, 3,5‐dimethyl‐N‐(3‐nitropyridin‐4‐yl)pyridin‐2‐amine ( 17 ), 3,5‐dimethyl‐N‐(5‐nitropyridin‐2‐yl)pyridin‐2‐amine ( 20 ), N‐(5‐nitropyridin‐2‐yl)pyridin‐2‐amine ( 24 ), 5‐methyl‐N‐(5‐nitropyridin‐2‐yl)pyridin‐2‐amine ( 23 ) and 3‐methyl‐N‐(5‐nitropyridin‐2‐yl)pyridin‐2‐amine ( 25 ) in 65 ‐ 80 % yield, obtained by cycloaddition, rearrangement and decarboxylation. The results demonstrate that the nitropyridyl isocyanates ( 7,9 ) readily undergo 1,3‐dipolar cyloaddition reactions similar to phenyl isocyanates.     

1,3‐dipolar cycloaddition reactions of nitrile oxides to prop‐1‐ene‐1,3‐sultone

The reaction of prop‐1‐ene‐1,3‐sultone 1 with a variety of nitrile oxides 3 afforded novel [3+2] cycloaddition products 4 in good yield. The cycloaddition reaction achieved excellent regioselectivity.     

Enantioselective radical allylation reactions using chiral lanthanide Lewis acids

Radical additions to oxazolidinone acrylate followed by allyl trapping were studied with chiral Lewis acids derived from lanthanide salts. Chiral ligands were evaluated to establish the -stereocenter. Ligands with a prolinol framework along with achiral additives proved to be effective. The observed trends are compared with those in the literature.     

Synthesis and 1,3‐dipolar cycloaddition reactions of N‐Aryl‐C,C‐dimethoxycarbonylnitrones

Arylnitroso compounds 1–3 easily reacted with dimethyl bromomalonate to give the corresponding N‐aryl‐C,C‐dimethoxycarbonylnitrones ( 4–6 ). Treatment of C,C‐dimethoxycarbonyl‐N‐( 1‐naphthyl)nitrone ( 4 ) with acetylene compounds (dimethyl acetylenedicarboxylate, methyl 2‐butynoate or ethyl phenylpropiolate) caused 1,3‐dipolar cycloaddition to furnish the corresponding 1H‐benz[g]indolines ( 7a‐c ). In a similar manner, the reactions of nitrones 5 and 6 with acetylene compounds afforded the corresponding indolines 9a‐c and 11a‐c together with 4‐oxazolines 13a‐c and 14a‐c .     

2‐Pyrazolines from 1,3 ‐ dipolar cycloaddition of diazomethane to arylsulfonylethenes

Novel 2‐pyrazolines were obtained by the cycloaddition of diazomethane to bis(arylsulfonylethenyl)‐sulfones ( 3 ) and 1‐arylsulfonyl‐2‐styrylsulfonylethenes (7). Dehydrogenation of 2‐pyrazolines with chloranil gave pyrazoles.     

Regio‐ and stereoselective synthesis of isoxazolidine derivatives by asymmetric 1,3‐dipolar cycloaddition reaction of chiral nitrones with 1‐propene‐1,3‐sultone

Asymmetric 1,3‐dipolar cycloadditions of chiral nitrones to 1‐propene‐1,3‐sultone ( 1 ) were investigated. Chiral nitrones 6a‐e reacted with sultone 1 in toluene at 90 °C for 24‐36 h to give the corresponding isoxazolidines in moderate yields with high regioselectivities and stereoselectivities. The diastereoselectivity of this reaction varied with the choice of dipolarophile and the steric demands of nitrones. When sultone 1 was allowed to react chiral nitrone 6e , a much better diastereoselectivity of up to 5.1:1 was observed.     

MgSiO3 nanoparticle‐catalyzed 1,3‐dipolar cycloaddition reactions in the synthesis of novel spiroindane‐1,3‐diones derived from substituted chalcones

Employment of metal nanoparticles has been one of the most promising synthetic strategies for a number of chemical transformations. New spiroindane‐1,3‐diones were synthesized through [3 + 2] cycloaddition in moderate to high yields by a three‐component reaction of heterocyclic chalcone derivatives, ninhydrin, and sarcosine/L‐proline. The presence of heterogenous MgSiO₃ nanoparticles (NPs) under microwave irradiation showed a robust effect in improving the yield of the desired products. Furthermore, the catalyst may be recovered and reused without significant loss of activity.     

An efficient one‐pot synthesis of dispiropyrrolidine derivatives through 1,3‐dipolar cycloaddition reactions under ultrasound irradiation

A series of dispiropyrrolidine derivatives were synthesized via the three‐component 1,3‐dipolar cycloaddition reaction of isatin, sarcosine and 5‐arylidene‐1,3‐thiazolidine‐2,4‐dione or 5‐arylidene‐4‐thioxo‐1,3‐thiazolidine‐2‐one in ethanol under ultrasound irradiation. This protocol has the advantages of mild reaction conditions, higher yields, and shorter reaction time. J. Heterocyclic Chem., (2011).     

Inverse electron‐demand 1,3‐dipolar cycloaddition reactions of cyclooctyne with pyridinium bis(methoxycarbonyl)methylides

Cyclooctyne underwent 1,3‐dipolar cycloaddition with pyridinium bis(methoxy‐carbonyl)methylides to afford the corresponding indolizines (8‐methoxycarbonyl‐7‐azatricyclo[7.6.0.0^2‐7]pentadeca‐1,3,5,8‐tetraenes) in good to moderate yields. Some molecular orbital considerations are also described on this reaction compared with the results on the reaction of pyridinium dicyanomethylides with cyclooctyne.     

Reactivity of 2‐methylene‐1,3‐dicarbonyl compounds. 1,3‐dipolar cycloaddition reaction with nitrile oxide

The reaction of 2‐methylene‐1,3‐dicarbonyl compounds 1 and nitrile oxides, which were prepared from hydroxymoyl chlorides 2 with triethylamine, gave 5,5‐disubstituted 2‐isoxazolines 3 regioselectively.     

Enantioselective carbon–carbon bond forming reactions using fluorous chiral catalysts

Fluorous chiral BINOLs and BINAP were prepared and used as the ligands for an asymmetric addition of Et₂Zn to aromatic aldehydes and an asymmetric Heck reaction, respectively. The enantioselectivities were similar in homogeneous system to those of the original non-fluorous reactions. Consecutive reactions were examined by utilizing fluorous–organic biphase and fluorous solid phase extraction techniques. Enantioselectivities in consecutive reactions were close to that attained in the non-fluorous system. The solid phase extraction method also enabled us to perform a simultaneous screening procedure.     

Three‐component 1,3‐dipolar cycloaddition reactions in synthesis of spiro[pyrrolidine‐2,3′‐oxindoline] derivatives

Regio‐ and stereospecific syntheses of several spiro[pyrrolidine2,3′‐oxindole] derivatives by cycloaddition trapping of azomethine ylides generated in situ, via decarboxylative condensation of isatin with α‐amino acids or by reaction of secondary amines with isatin, are reported. 2,6‐Dibenzylidenecyclohexanone, 2‐arylidene‐1‐tetralone, and arylidenemalononitrile derivatives have been efficiently used as trapping dipolarophiles. The regio‐ and stereochemistry of the additions are controlled by both frontier orbital and steric interactions. © 2002 Wiley Periodicals, Inc. Heteroatom Chem 13:324–329, 2002; Published online in Wiley Interscience (www.interscience.wiley.com). DOI 10.1002/hc.10038     

Reversible 1,3‐dipolar cycloaddition of dimethyl 2‐thiono‐1,3‐dithiole‐4,5‐dicarboxylate with dimethyl acetylenedicarboxylate

It was shown that dimethyl 2‐thiono‐1,3‐dithiole‐4,5‐dicarboxylate ( 2 ) and dimethyl acetylenedicarboxylate (DMAD) undergo a 1,3‐dipolar cycloaddition to produce a short‐lived ylide intermediate ( 3 ). The 1,3‐dipolar cycloaddition took place even at room temperature, although sluggishly, but took place much more rapidly under application of a high pressure of 500 MPa. The 1,3‐dipolar cycloaddition is reversible and the ylide 3 immediately splits into 2 and DMAD. When the reaction of 2 with DMAD was carried out at room temperature without solvent, a spiro‐1,3‐dithiole ( 11 ) was formed in 11% yield, whereas the reaction at 150°C provided a thiophene derivative ( 13 ) in 41% yield. It was found that 11 undergoes a thermal rearrangement to 13 . Results of attempted chemical trapping of the ylide 3 are also reported. © 2000 John Wiley & Sons, Inc. Heteroatom Chem 11:434–440, 2000     

Novel syntheses of polysubstituted pyrroles and oxazoles by 1,3‐dipolar cycloaddition reactions of benzotriazole‐stabilized nitrile ylides

1,3‐Dipolar cycloadditions of benzotriazole‐stabilized nitrile ylides with benzyl α,β‐unsaturated‐carboxy‐lates and aldehydes as dipolarophiles proceeded smoothly and efficiently to give polysubstituted pyrroles and oxazoles, respectively, in good yields.     

Synthesis of potentially photoactivatable coumarin derivatives via a 1,3‐dipolar cycloaddition

A copper (1)‐catalyzed 1,3‐dipolar cycloaddition reaction was used to prepare a series of mono and disubstituted 1,2,3‐triazolyl‐coumarins using a 1,3‐cycloaddition (“Click Chemistry”). Starting coumarins were synthesized using classical or modified Pechmann's reaction. The propargyl group was introduced as either propargylether or as a propargylamide. Azides were prepared in a three steps procedure. Cycloaddition products, containing a coumarin and a photoactivatable moiety, were obtained in good yields.     

A regioselective 1,3‐dipolar cycloaddition of 2‐arylidene‐1‐tetralones with DPNI

Synthesis of a series of novel 1,3‐diphe nyl‐4‐arylspiropyrazolines[5.2¹]‐1¹‐tetralones has been accomplished in good yield by regioselective 1,3‐dipolar cycloaddition of diphenylnitrilimine with (E)‐2‐arylidene‐1‐tetralones. X‐ray crystal structure analysis of one of the products 4b confirms the structure and the regiochemistry of cycloaddition. © 1999 John Wiley & Sons, Inc. Heteroatom Chem 10: 331–336, 1999