Extrusion of dinitrogen

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). 

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. ... 

Compared to the cycloadditions of nitroalkenes, tandem cycloadditions of 1,3,4-oxadiazoles consist not of two, but of three elementary reactions. In the first step, a 1,3,4-oxadiazole 428 serves as an electron-poor heterodiene (4jt-component) and reacts thermally with an alkene dienophile (2jt-componait) by a [4-1-2] cycloaddition reaction. The preferred dienophile is electron-rich, unhindered, and strained. At the elevated temperatures required for the first step [169], the immediate product of this reaction, 430, is unstable and undergoes extrusion of dinitrogen by a [3 + 2] cycloreversion to form dipole 431 [170]. At the high temperatures required for its formation, 431 cannot be directly observed either and reacts by a [3 + 2] cycloaddition with an available dipolarophUe, which can be the same 27i-component that served as the dienophile or something else. Because none of the intermediates is isolated and no change in reaction conditions is required, tandem [4-f 2]/[3- -2] cycloadditions of 1,3,4-oxadiazoles are tandem cascade processes as defined earlier in this chapter. 

Myers crafted a process involving a 1,5-H shift for the stereospecific synthesis of optically active allenes from propargylic alcohols (Scheme 16.31) [119, 120], Mitsonobu displacement of the alcohol in 229 by arylsulfonyl-hydrazine 230 afforded 231. At ambient temperature, elimination of sulfinic acid occured, and the resulting diazine 232 underwent extrusion of dinitrogen and 1,5-H-shift to afford allene 233 [119]. The sequence has been demonstrated to be enantiospecific, affording optically active allenes such as... 

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