Ylides generation

Benzoxepin (4) was obtained in 55% yield by the reaction of phthalaldehyde with the bis-ylide generated from the bis(triphenylphosphonium) salt prepared from bis(bromomethyl) ether and triphenylphosphane.93,94... 

Treatment of the bis-ylide generated from bis 2-[(triphenylphosphonio)methyl]phenyl ether and sodium amide with oxygen gives dibenz[A./]oxepin (3) in 50% yield.98 99... 

An elegant procedure for the synthesis of 5//-dibenz[c,e]azepines 14, which is an extension of the procedure outlined at the beginning of this section, has been developed in which the nitrile ylides, generated by the treatment of iV-(2-arylbenzyl)benzimidoyl chlorides 12 with potassium /er/-butoxide, undergo a 1.7-electrocyclization at the adjacent phenyl ring, followed by a hydrogen shift 13 - 14.102... 

More recently carbonyl ylides and the corresponding imino ylides generated from aryl- and vinyldiazoacetates have been shown to undergo a variety of processes not previously encountered (Scheme 12) [112,113]. The difference in... 

Tandem ammonium ylide generation-rearrangement reactions... 

The regio- and stereochemical outcome of the intermolecular 1,3-dipolar cycloaddition of an azomethine ylide generated by the decarboxylative condensation of an isatin with an a-amino acid was unambiguously determined by a single-crystal X-ray study of the spirocyclic heterocycle 49 (R1 =4-Br, R2 = H, X = CH2) <1998TL2235>. 

The feasibility of azomethine ylide generation from 7 and intramolecular dipolar cycloaddition was examined under a variety of conditions. For example, activation of vinylogous amide 71 with BzOTf [41] followed by desilylation with TBAT led to complex mixtures of products. Likewise, using MeOTf as the activating agent yielded similar results. Significantly, none of these protocols furnished the desired pyrrolidine 73. Only decomposition of the silylpyridinone to form unidentified products was observed, despite the fact that quantitative O-methylation of the... 

Our first entry to the use of porphyrins as dipolarophiles in 1,3-DC reactions involved the reaction of porphyrins with azomethinic ylides, generated in situ from a-amino acids and aldehydes, to yield chlorins and isobacteriochlorins (bisadducts) <99CC1767, 05JOC2306>. 

In the particular scenario of the reaction of ie.vo-tctrakis(pcntafluorophenyl)porphyrin Id with the azomethine ylide, generated in situ from /V-mcthylglycine and paraformaldehyde, in refluxing toluene during 15 hours, the pyrrolidinochlorin derivative 62 was obtained as the main product (Scheme 19), together with a small amount of isobacteriochlorin 63 (bis-adduct, Figure 5). 

Another example illustrating the versatility of 1,3-DC reactions is concerned with the reaction of [36]octaphyrin 71 with azomethine ylide generated in the usual way from N-methylglycine and paraformaldehyde, to give mono- and bis-pyrrolidine-fused adducts 72 and 73 (Scheme 25) <06OLl 169>... 

Hu and co-workers reported a facile synthesis of pyrrolo[2,l-n]phthalazine 205 by a 13-dipolar cycloaddition of phthalazium N-ylides generated from 203 with electron deficient alkenes to give 204, followed by treating 204 with tetrakispyridine cobalt(II) dichromate [Py4Co(HCr04)2, TPCD] to complete the aromatization <00JHC1165>. 

Reactions.—Aldehydes. The stereochemistry of the alkene produced from ylides generated by using 18-crown-6 complexes of potassium carbonate or butoxide, depends upon the solvent used. In THF typical salt free distributions are obtained whereas in dichloromethane reversal of product distributions is observed.17 A simplified method (Scheme 4) for preparing para-substituted styrenes in high... 

Dipolar cycloaddition of azomethine ylides, generated by the condensation of an a-amino acid and an aldehyde, is an efficient method for covalent sidewall functionalisation and has been successfully used to solubilise CNTs in most organic solvents (Tasis et al., 2003 Holzinger et al., 2003). This particular technique has also been utilised to obtain the first example of a bioactive peptide covalently linked to CNTs by the prospect for the potential applications in immunology (Bianco and Prato, 2003 Pantarotto et al., 2003a, b Bianco et al., 2005b). 

The scope of these reactions has not yet been thoroughly investigated. The examples listed in Table 4.17 suggest that azomethine ylides generated by intramolecular, carbene-mediated N-alkylation of imines enable convergent and fast... 

Fig. 4.16. Atypical reactions of carbonyl ylides generated from carbonyl compounds and acceptor-substituted carbene complexes [1276,1306],...

Interestingly, sulfonium ylides generated from electrophilic carbene complexes and sulfides can react with carbonyl compounds, imines, or acceptor-substituted alkenes to yield oxiranes [1320-1325], aziridines [1321,1326,1327] or cyclopropanes [1328,1329], respectively. In all these transformations the thioether used to form the sulfonium ylide is regenerated and so, catalytic amounts of thioether can be sufficient for complete conversion of a given carbene precursor into the... 

Thus, allyl telluronium ylides generated in situ from the corresponding telluronium salts in the presence of Li salts react with a,)3-unsaturated esters and amides to afford trans-2-vinyl-/rany-3-substituted cyclopropyl compounds in high yieds. 

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