Cycloaddition with

The cyclooctenonecarboxylate 169 undergoes smooth cycloaddition with 154 to give 170 in a good yield, but no reaction takes place with cyclooctenone (171)[111], Cyclohexenone behaves similarly. Cycloheptatrienone (172) undergoes [6-1-3] cycloaddition to form the nine-membered carbocycle 173[112],... 

This category corresponds to the construction of the carbocyclic ring by 2 + 4 cycloaddition with pyrrole-2,3-quinodimethane intermediates. Such reactions can be particularly useful in the synthesis of 5,6-disubstituted indoles. Although there are a few cases where a pyrrolequinodimethane intermediate is generated, the most useful procedures involve more stable surrogates. Both 1,5-di-hydropyrano[3,4-b]pyrrol-5(lf/)-ones[l] and l,6-dihyropyrano[4,3-b]pyrrol-6-(in)-ones[2] can serve as pyrrole-2,3-quinodimethane equivalents. The adducts undergo elimination of CO2. 

Indoles by cycloaddition with pyrrole-2,3-quinodimethane equivalents... 

Reactivity involving the mesoionic protomer has been investigated very recently (562). It was known that fixed mesoionic structures undergo cycloaddition with various dipolarophiles (473) and that such a reactivity Ph. 

Acylisocyanates or isothiocyanates undergo cycloaddition with 5-hydroxy-THISs under so mild conditions that isolation of the initial adducts becomes possible (23). In cycloaddition reactions the 5-hydroxy-THISs can be replaced by their precursors (23). 

It is, however, possible to perform reactions such as hydrogenation, halogenation, polymerization, and [2 + 2] cycloadditions with the exocycHc... 

Concerted Nonpolar Reactions. Maleic anhydride exemplifies the model dienophile for cycloaddition with dienes such as 1,3-butadiene... 

The diene undergoes Diels-Alder cycloaddition with dienophiles. Polyimides have been synthesized from various imide-containing benzocyclobutenes and dienophiles (83—85). 

Reaction of arninoacetonitrile hydrochloride with sodium nitrite provides diazoacetonittile (62). The product undergoes a 1,3-dipolar cycloaddition with diethyl fumarate to yield a pyrazoline intermediate, which without isolation reacts with ammonia in water to furnish the pyrazole [119741-54-7] (63) (eq. 14) (43). 

Pyrrole 1-oxides are known they undergo 1,3-dipolar cycloaddition with DMAD and with A-phenylmaleimide (80TL1833). 

As the sp nitrogen atom in many heterocycles can be alkylated and aminated, the construction of an azomethine ylide or azomethine imine dipole is readily attainable as shown in Scheme 13. These ylides are very reactive and undergo cycloaddition with a... 

A newer method for the preparation of nitronic esters, namely utilizing the (9-trimethyl-silyl ester, has been reported and these are prepared by the reaction of alkylnitro compounds and (V,(V-bis(trimethylsilyl)acetamide. These nitronic esters also undergo cycloaddition with alkenes to produce isoxazolidines (equation 54) (74MIP41601, 74DOK109, 78ACS(B)ll8). 

Chlorination of sodium cyanodithioformate gives 3,4-dichloro-5-cyanoisothiazole (227), probably via the isothiazolodithiine (226) (72AHC(l4)l). The thienoisothiazole (228) undergoes cycloaddition with alkynic esters to give adducts such as compound (229), which... 

The 27T-electrons of the carbon-nitrogen double bond of 1-azirines can participate in thermal symmetry-allowed [4 + 2] cycloadditions with a variety of substrates such as cyclo-pentadienones, isobenzofurans, triazines and tetrazines 71AHC(13)45). Cycloadditions also occur with heterocumulenes such as ketenes, ketenimines, isocyanates and carbon disulfide. It is also possible for the 27r-electrons of 1-azirines to participate in ene reactions 73HCA1351). 

The interaction of diazomethane with 1-azirines was the first example of a 1,3-dipolar cycloaddition with this ring system (64JOC3049, 68JOC4316). 1,3-Dipolar addition produces the triazoline adduct (87). This material can exist in equilibrium with its valence tautomer (88), and allylic azides (89) and (90) can be produced from these triazolines by ring cleavage. 

Aziridines, e.g. (91), undergo thermal ring opening in a conrotatory manner to generate azomethine ylides. These azomethine ylides are 47r-components and can participate in [4 + 2] cycloadditions with 1-azirines acting as the 27r-component 73HCA1351). 

The following compounds have been obtained from thiete 1,1-dioxide Substituted cycloheptatrienes, benzyl o-toluenethiosulfinate, pyrazoles, - naphthothiete 1,1-dioxides, and 3-subst1tuted thietane 1,1-dioxides.It is a dienophile in Diels-Alder reactions and undergoes cycloadditions with enamines, dienamines, and ynamines. Thiete 1,1-dioxide is a source of the novel intermediate, vinylsulfene (CH2=CHCH=SQ2). which undergoes cyclo-additions to strained olefinic double bonds, reacts with phenol to give allyl sulfonate derivatives or cyclizes unimolecularly to give an unsaturated sultene. - Platinum and iron complexes of thiete 1,1-dioxide have been reported. 

Perfluoroisobutylene undergoes cycloadditions with azides only at elevated temperatures, the reaction can lead to subsequent loss of nitrogen [6] (equation 4) In another high-temperature reaction, chlorotrifluoroethylene undergoes cy cloaddition with the azomethineylide generated from the thermal electrocyclic nng opening of an azindine, a reaction that contributes to a good overall synthesis of 3,4-difluoropyrroles [7] (equation 5)... 

Lastly, perfluoropropyne undergoes cycloaddition with diphenyldia-zomethane to give a single product, although the regiochemistry is undetermined... 

On the other hand, its cycloadditions with 1,2-disubstituted alkenes under similar conditions produce stereospecifically a mixture of regioisomeric products [35] (equation 34) In contrast, its reaction with theunsymmetrical alkyne 1 -phenyl-propyne leads to a single product [35] (equation 35)... 

Recently, Burger devised an improved method of carrying out mild, regiospecific cyclizations that involve an intermediate that acts as a synthon for a nitrile ylide of HCN [47 (equation 48). With this methodology, cycloadditions with activated alkenes, alkynes, and azo compounds were earned out [47] (equation 49). All such reported reactions were regiospecific and had the same orientational preference... 

Nitrone hydrate is converted into nitrone by boiling in benzene with azeotropic removal of water [48] (equation 50). This in situ formation of nitrone is carried out in the presence of various alkenes and alkynes, which undergo cycloaddition with the nitrone [48, 49] (equations 51 and 52). 

Bis(trifluoromethyl)-l,l-dicyanoethylene is a very reactive dienophile. It undergoes facile and high-yield [2+4] cycloadditions with 1,3-dienes, cyclopen-tadiene, and anthracene [707] (equation 86). It is reactive enough in a Diels-Alder reaction with styrene [702] (equation 86). 

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