Dinitrogen, extrusion

Chiral Rh(II) oxazolidinones Rh2(BNOX)4 and Rh2(IPOX)4 (25a,b) were not as effective as Rh2(MEPY)4 for enantioselective intramolecular cyclopropanation, even though the steric bulk of their chiral ligand attachments (COOMe versus i-Pr or CH2Ph) are similar. Significantly lower yields and lower enantioselectivides resulted from dinitrogen extrusion from prenyl diazoacetate catalyzed by either Rh2(4.S -lPOX)4 or Rh2(4S-BNOX)4. This difference, and those associated with butenolide formation [91], can be attributed to the ability of the carboxylate substituents to stabilize the carbocation form of the intermediate metal carbene (3b), thus limiting the Rh2(MEPY)4-catalyzed reaction to concerted carbene addition onto both carbon atoms of the C-C double bond. 

Scheme 1.2. Regioselective formation of chiral hexakis- and octakis-adducts of C6o by repeated addition of diazomethane to a C2V-symmetric pentakis-adduct, followed by thermal dinitrogen extrusion.

Addition of a-diazoketones derived from (W, A )-tartaric and (S )-glutamic acids, followed by dinitrogen extrusion, afforded enantiomerically pure 1,2-methano[60]fullerenes with an acylated methylene bridge.441 Bestmann and co-workers showed that these adducts can be thermally rearranged to substituted fullerene-fused dihydrofurans. 

Analogous to the preparation of (33), the cycloaddition of two equivalents of tri-ra-butyl (ethynybtin to 2,6-bistriazinylpyridine affords the 4,4"-di-(tri- -butyl)stannane (43b) after dinitrogen extrusion. 

Cyclopropanation of tricarbonyl(tropone)iron 18 via cycloaddition of diazomethane, diazoethane or diazopropane and thermal dinitrogen extrusion gave bicyclo[5.1.0]octadienone ( homotropone ) complexes which decomposed to form the free ligand 20 in high yield. When the same procedure was applied to the free ligand 16, a substituted cyclooctatrienone system 17 was obtained via ring expansion. 

The intramolecular 3 + 2-cycloaddition of iV-(2-azidomethyl)phenyl ketenimines (48) and iV-(2-azidomethyl)phenyl-iV -alkyl(aryl) carbodiimides (49) produced cycloadducts (50) and (51), which underwent dinitrogen extrusion to form indolo[l,2-fljquinazolines and tetrazolo[5,l-fe]quinazolines, respectively, under mild thermal conditions (Scheme 15). ... 

The 2,5-dihydro-l,3,4-thiadiazole 79 reacts with a range of acetylenic dipolarophiles to afford the 2,5-dihydrothio-phenes 80 in 25-75% yields (Equation 19) <2002HCA451>. The thermal extrusion of dinitrogen from the thiadia-zole affords a thiocarbonyl ylide, which reacts with the dipolarophiles to form the thiophenes. 

Intramolecular C-N bond coupling in arylazides via C-H bond activation catalyzed by [Ir(COD)(OMe)]2 was recently reported [131]. The intermediate iridium nitrenoid complex (50) formed after the extrusion of dinitrogen is proposed as a reactive species, which can cleave the benzylic C-H bond to yield indoline derivatives (31). 

Reactions of Oxazoles. 2-, 4-, and 5-Nitro-oxazoles can be prepared by the action of dinitrogen tetroxide on the corresponding iodo-compounds. Whereas oxazoles are metallated at C-5, the acid (371) undergoes lithiation at the methyl substituent.The reaction of 2,4-dimethyloxazole with ethyl propiolate yields a mixture of the furans (373) and (374) these are formed by extrusion of acetonitrile from intermediate Diels—Alder adducts such as (372). s3... 

The seven-metnbered ring sultam (32) is nitrosated smoothly on the ring nitrogen by reaction with dinitrogen tetraoxide to afford (33) the decomposition of this and other JV-nitrososultams can then be studied, in particular the formation of the sultones (e.g., (34)) with nitrogen extrusion in the presence of base (Scheme 2) <87JOC2l62>. 

Alkyl-, vinyl-, and aryl-substituted acyl azides undergo thermal 1,2-carbon-to-nitrogen migration with extrusion of dinitrogen — the Curtius rearrangement — producing isocyantes. Reaction of the isocyanate products with nucleophiles, often in situ, provides carbamates, ureas, and other A-acyl derivatives. Alternatively, hydrolysis of the isocyanates leads to primary amines. 

An interesting Cu(I)-catalyzed annulation of tethered pyrroloalkynes 365 and 367 into amino-substituted N-fused pyrroloheterocycles 366 and 368, respectively, was recently demonstrated by Chang (Scheme 9.128) [306]. This reaction was proposed to proceed through a ketenimine intermediate 370, which in turn was generated in situ from the 1,2,3-triazole cycloadduct 369 upon extrusion of dinitrogen (Scheme 9.129). 

Like other pyrazolines, 4-methylene-1-pyrazoline (MP) undergoes thermal extrusion of dinitrogen to form methylenecyclopropane (MCP) [35], but it does so much more rapidly the energy of activation is about 9 kcal/mol lower than that of the parent 1-pyrazoline, more than enough to offset a hundredfold reduction in the pre-exponential factor [40, 41]. This kinetic behaviour is prima facie evidence that the reaction proceeds stepwise via a triplet intermediate. The obvious choice was trimethylenemethane (TMM), that had been shown to have a triplet ground-state [36, 37, 38], in confirmation of numerous theoretical predictions [39], [18, pp. 141ff.j. 

Thermal extrusion of dinitrogen from the adduct of benzene with diazomethane, and from the pyrazoline adducts of fullerenes with diazoalkanes (to give 6-5-open methanofullerenes), are believed to feature a Mobius aromatic transition state with a highly anisotropic magnetic susceptibility. ... 

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