Extrusion of carbon dioxide

In an interesting reaction, pyrrolysis of the urethane leads to extrusion of carbon dioxide and formation of 23, propiomazine Although this agent contains the ethylenediamine side chain, its main use is as a sedative. 

Whereas electronically activated 2-pyrones can react thermally in both normal and inverse electron-demand Diels-Alder cycloaddition, 2-pyrone by itself requires thermal conditions that are so vigorous that they cause spontaneous extrusion of carbon dioxide from the bicyclic cycloadduct [61]. 

Phenylsydnone 89 is not restricted to [3+2] cycloaddition. Reaction of sydnone 89 and its derivatives with the substituted azete 90 gives isomeric l//-triazepines after extrusion of carbon dioxide (Equation 8). 

Nair and coworkers have described the [8 + 2] cycloaddition reactions of 2H-cyclohep-ta[fr]furan-2-ones such as 521 in several reports311. The reactions of 521 with alkenes yield azulene derivatives upon extrusion of carbon dioxide. Table 30 summarizes the results of the reactions between 521 and some 6,6-disubstituted fulvenes 522 (equation 151)311b. In the case of 6,6-dialkyl fulvenes 522a-c, the [8 + 2] cycloadducts 523 were the major adducts obtained, the Diels-Alder adducts 524 only being formed in trace amounts. 

The most probable mechanism for the reduction requires the initial nucleophilic attack by the hydridometal complex on the nitro group, followed by intramolecular cyclization and extrusion of carbon dioxide. Repetition of the cyclization and extrusion sequence, followed by proton transfer, leads to aniline (Scheme 11.6). 

The mesoionic compound prepared from L-Pro (83TL1067) reacts with acetylenic compounds to give pyrrolo[l,2-a]pyrazoles after extrusion of carbon dioxide ( Scheme 47). With phenylpropiolic acid, the natural product withasomnine (a) was formed in low yield (7%) together with its regioisomer (b, 5%) (85TL5739). 

In analogy with 143d, the 2-phenyl compound is obtained from tropone and 3-phenylsydnone in a low yield [93JCS(P1)1617]. The cycloaddition proceeds peri- and regioselectively in a [4it + 2tt] mode followed by extrusion of carbon dioxide from the primary adduct and spontaneous dehydrogenation. 

Flash vacuum pyrolysis of 2-phenyl-5(4F/)-oxazolone 146 effects extrusion of carbon dioxide to produce 3-phenyl-2//-azirine 290 in moderate yield (Scheme 7.95). ... 

Thermal studies on l,3-oxazetidin-2-ones, as expected, show the major pathway to be extrusion of carbon dioxide to give imines (70BAU1479,80S571). These systems are surprisingly stable for example, for (V-phenyl-l,3-oxazetidin-2-one AH = 128.9 kJ mol-1 and AS = 54.4 J K-1 mol . There is one report of fragmentation to give ketone and isocyanate... 

Extrusion of carbon dioxide and sulfur was also used by Barton [441], as in the following example ... 

Intermolecular nitrile sulfide cycloadditions have been known for some time but the first intramolecular cycloadditions have just been reported.132 The oxathiazolone (243) gave (244a) in 70% yield when heated in refluxing xylene (Scheme 71). Extrusion of carbon dioxide presumably afforded the nitrile sulfide as an intermediate. The oxathiazolone (245) gave (244b) when heated in refluxing xylene here, aro-matization of the initial cycloadduct presumably occurred. 

S. Yamada, H. Ishikawa, and M. Matsumoto, An unusual photochemical extrusion of carbon dioxide from laevoglucosenone derivatives via carbene intermediates, J. Chem. Soc., Chem. Commun., (1994) 2155-2156. 

Thermolysis of readily prepared telluroformates 115 leads to scission of the bond between tellurium and the carbonyl group. Extrusion of carbon dioxide leads to a radical cyclization affording 2-substituted selenanes 116 (Scheme 8) C1996JOC5754, 1998JOC3032>. 

The preparation of metal nitrides with N3 reagents typically employs d° metal complexes as starting materials. However, the reactions of r-butyl isocyanate with metal-oxo complexes of OsVI and RuVI represent rare examples of the use N3- reagents with d2-metals. It has been postulated that reaction of the isocyanate with metal-oxo 3 affords a four-membered ring intermediate 4, followed by the extrusion of carbon dioxide to yield r-butyl metal imide 5 (Scheme 1). Elimination of isobutylene from this complex then produces the metal nitride and the isobutylene. 

Oxazole N-oxides having a 4-methyl substituent are attacked by acetic anhydride to yield 4-acetoxyoxazoles (equation 21). The combined action of benzoyl chloride and potassium cyanide leads to compounds of the Reissert type, e.g. (177). The reaction of 4-methyloxazole Yoxides with phenyl isocyanate gives 5-hydroxy-4-methylene-l-phenyl-4,5-dihy-droimidazoles by cycloaddition, extrusion of carbon dioxide and recyclization (Scheme 12) with 4-phenyloxazole JV-oxides the reaction takes a different course, yielding imi-dazooxazolidinones (Scheme 13). 

The use of a nonnucleophilic base affects the dehydrobromination and the corresponding diene lactone 6 may be formally considered a [2 + 2] cycloadduct of a substituted benzene and carbon dioxide that, through the extrusion of carbon dioxide affords the aromatic compound 7. Heating the olefinic bromo-/ -Iactone 5 in a Kugelrohr apparatus leads to a stereoselective 1,2 bromide migration with concomitant expansion of the lactone to its thermodynamically more stable y-isomer 8. 

A final example of a rDA cycloreversion of a cycloadduct that acts as a protected butadiene illustrates the generation of extended conjugation in a non-aromatic cyclic system. Equation (65) shows that the addition of cyclopropene (147) to (146) can yield either (148) or (149), and both adducts undergo rDA extrusion of carbon dioxide to produce a triene. Hydrolysis of the triene ketals gives access to substituted tropones (150). 

Extrusion of carbon dioxide to give cyclopropyl ketones has been observed in the treatment of 2-acylbutanolides with a halide salt in DM SO or DMF (equation 8). 4-Aryl-or 4-alkenylbutenolides also expel CO2 photochemically. Irradiation of cyclobuta-nones with UV light often gives cyclopropanes by loss of carbon monoxide . In this... 

During experiments to trap a reaction product of a nitroso compound and isonitrile with an alkyl isocyanate, an additional way of formation of diaziridinimines was discovered. Besides some other heterocycles the five-membered ring compound 138 was formed, which yielded 133 by extrusion of carbon dioxide at 150°. ... 

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