Nitrones isoxazolidine ring

As for the regioselectivity of the nitrone cycloaddition to MCP and its alkyl or aryl derivatives, a tendency of the three-membered ring to end up at the 4-position of the final isoxazolidine ring clearly emerges from the experimental findings. This result is particularly noteworthy if compared to regiospecific formation of the 5,5-disubstituted isoxazolidines in the reactions of nitrones, not... 

Also, the effectiveness of 1,3-dipolar cycloadditions to a,p-unsaturated 8-lactones D7a, D7c, D7 d (784) and D7f, (785) in controlling the configuration of the stereogenic centers around the formed isoxazolidine ring, was demonstrated in reactions with nitrones (595). 

The addition of nitrones (647) and (312) to 4-pentenofuranoside (648) derived from D-ribose, followed by reductive opening of the isoxazolidine ring in (649)... 

Intramolecular nitrone-alkene cycloaddition. Reaction of cycloalkanones substituted by a 3-(2-propenyl) or a 3-(3-butenyl) side chain with alkylhydroxylamines with azeotropic removal of water results in a bridged bicycloalkane fused to an isoxazolidine ring. The transformation involves formation of a nitrone that undergoes intramolecular cycloaddition with the unsaturated side chain. 

Cycloaddition/cycloreversion processes were also employed to temporarily mask the reactive nitrone functionality <2002J(P1)1494, 2002EJ01941>. For example, nitrone 208 was protected by cycloaddition with styrene. The isoxazolidine ring remained unaffected during all the reaction steps used to introduce a pendant dipolarophile and obtain the derivative 209. By heating in a sealed tube at 190 °C, isoxazolidine 209 underwent cycloreversion restoring the nitrone moiety which was directly trapped by an intramolecular 1,3-dipolar cycloaddition to afford 210 with complete regio- and diastereoselectivity (Scheme 47). 

The photochemical behavior of the isoxazolidine ring is not extensively studied. Depending upon the experimental conditions, 5-nitroxazolidines undergo photolysis to yield either 4-isoxazolines by the elimination of nitrones or to P lactam derivatives, by ring opening followed by reclosure... 

If poly butadiene is caused to react with nitrones, the isoxazolidine ring is incorporated in the butadiene rubber chain. The carbon black-... 

Dipolar cycloadditions take place when nitrones or nitrile oxides add to butadiene rubber. Some of the products contain isoxazolidine rings [75] ... 

Isoxazolidine ring from nitrones—Ring closure with azomethinium betaines —Pyrazolidines from azomethinimines s. 16, 735... 

Catalyst -, Geo -, Metal -, Nucleophile -, Regio-, Stereo-, Wavelength -iryn-an z-Specificity -, isoxazolidine ring from nitrones 16, 735s31 Spirocyclopropane ring opening, double, paracyclophanes by -30, 472... 

Several bisphosphonates bearing a substituted isoxazolidine ring (731), have been synthesised in good yields by a direct 1,3-dipolar cyclisation reaction of tetraethylvinyhdene-l,l-bisphosphonate (730) and substituted nitrone (729), under microwave catalysis, in the absence of solvent (Scheme 185). ... 

Ring closure with azomethinium hetaines Pyrazolidines from azomethinimines Isoxazolidines from nitrones... 

We are the first group to succeed with the highly enantioselective 1,3-dipolar cycloadditions of nitronates [75]. Thus, the reaction of 5,6-dihydro-4H-l,2-oxazine N-oxide as a cyclic nitronate to 3-acryloyl-2-oxazilidinone, at -40 °C in dichloro-methane in the presence of MS 4 A and l ,J -DBFOX/Ph-Ni(II) complexes, gave a diastereomeric mixture of perhydroisoxazolo[2,3-fe][l,2]oxazines as the ring-fused isoxazolidines in high yields. The J ,J -DBFOX/Ph aqua complex prepared from... 

Lithiated epoxides have been found to react with a number of different activated electrophiles. A new study examines the reactivity of lithiated epoxides with nitrones to prepare 3,y-epoxyhydroxylamines, 46, and oxazetidine, 47 <06OL3923>. Upon deprotonation of styrene oxide, the lithiated reactant was then added to nitrone 45 to form the P,y-epoxyhydroxylamine 46 in good yield as a single diastereomer. A number of additional nitrones were examined as well and all provided similar yields of the 3,y-epoxyhydroxylamines. Treatment of 46 with additional base provided the 1,2-oxazetidine ring system 47 in excellent yield. Interestingly, none of the five-membered isoxazolidines from the 5-endo-tet cyclization were formed in this cyclization. 

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