Cumulated ylides

A number of preparations of cumulated ylides from methylenetriphenylphos-phorane have been described. Reaction with geminal dihalogenoalkenes,4 thiophos-gene,5 and dichloro-imines8 (ClaC=NR) gave (1), (2), and (3) respectively. 

Heterocycles.—The phosphonium salt (59) is an effective three-carbon synthon, as demonstrated by its reaction with enolates of /9-keto-esters (Scheme 20) to give cyclopentenyl sulphides via an intramolecular Wittig reaction.63 Ylides are also intermediates in the synthesis of dihydrofurans (60) from the cyclopropylphos-phonium salt (61) and sodium carboxylates (Scheme 21).64 Cumulated ylides are very useful for the synthesis of heterocyclic compounds, e.g. (62), from molecules which contain both an acidic Y—H bond and a carbonyl or nitroso-function, as shown in Scheme 22.65... 

The addition of a cumulated ylide to a salicylaldehyde leads to a coumarin (Scheme 128) <76AG(E)115>. 

Five- to seven-membered O-, N-, and S-heterocycles Acyl ylides with a tethered terminal ester function requisite for the construction of five- to seven-membered heterocycles are very conveniently accessible by reaction of the cumulated ylide ketenylidenetriphenylphosphorane 11 with various carboxylic esters bearing OH-, NHR-, and SH-groups in a-, -, or y-position. 

The reactions with sulfur or selenium result in the formation of betaines, which can be alkylated to give semi-ylide salts (equation 98). The reactions of hexaphenylcarbodiphosphorane with a series of heteroallenes also lead to betaines which on thermolysis yield new cumulated ylides (equation 99, cf. equation 120). 

Addition of an electrophile to the lone pair of oxo-, thioxo- and imino-vinylidenephosphoranes transforms the nucleophilic system into the dipolar ir -ir system of a ketene. The resulting phosphonium salt becomes a true dipolar ketene which, as such, reacts in a known manner (equation 101). Whenever the anion Nu is a stronger nucleophile than the original cumulated ylide, the new alkylidene-phosphorane will be formed, in which compound ElNu has added to the parent vinylidenephosphorane. If the starting phosphacumulene ylide is a stronger nucleophile than Nu , the intermediate salt always reacts with a second molecule of unreacted ylide in a [2 + 2] cycloaddition to give 1,3-cyclobutanedione derivatives. 

Imino derivatives 100 of compounds of type 95 were also directly prepared from cumulated ylides 82 or 4 and parabanic acid derivatives 99 by a presumed mechanism as depicted in Scheme 22 [70]. Attack of the nucleophilic ylidic carbon atom at the most electrophilic amide-type carbonyl carbon atom, ring opening with loss of phenyl isocyanate, and recyclization by N-C bond formation are the key steps. This reaction is reminiscent of an older one, furnishing 5,5-diethoxy- l-thiobenzoyl-4-triphenylphosphoranylidene-pyrrolidine-2,3-dione 102 from 2-phenylthiazoHne-4,5-dione 101 and 4 [71] in modest yield. 

Among the novel sulphonium ylides synthesized in this period are (8), (9) (which is unusually basic), (10), McgS—CHPO(OMe)2, EtMeS—C=CHS-MeEt (a cumulated ylide), and (11). ... 

Eacile approach to highly functionalized N-, 0-, and S-heterocycles using cascade syntheses with cumulated phosphorus ylides 98MI25. 

These carbene (or alkylidene) complexes are used for various transformations. Known reactions of these complexes are (a) alkene metathesis, (b) alkene cyclopropanation, (c) carbonyl alkenation, (d) insertion into C-H, N-H and O-H bonds, (e) ylide formation and (f) dimerization. The reactivity of these complexes can be tuned by varying the metal, oxidation state or ligands. Nowadays carbene complexes with cumulated double bonds have also been synthesized and investigated [45-49] as well as carbene cluster compounds, which will not be discussed here [50]. 

Heating a-hydroxy amides 135 in xylene with the cumulated phosphoms ylide 134 gives the 2(3//)-oxazolones 140. The reaction proceeds via an addition-cyclization-intermolecular-Wittig olefination sequence, which imphes three different types of phosphorus ylides, 134,136, and 137, respectively, of increasing ylide activity (Fig. 5.33 Table 5.7, Figs. 5.34, 5.35). 

A cumulated arsonium ylide has been prepared by reaction of a methoxycarbonyl arsonium ylide with sodium bis(trimethylsilyl)amide (equation 34) °. This ylide undergoes... 

A full account has appeared of the alkylation of the ester phosphorane Ph8p= CHC02Et with triethyloxonium borofluoride and of the reactions of the resulting ylide Ph3P=C=C(OEt)2- The cumulated phosphoranes (36) and... 

A more recent report discussed a microwave-assisted tetronate synthesis entailing domino addition/Wittig olefinations of polymer-bound a-hydroxy esters with the cumulated phosphorus ylide Ph3P=C=C=0 [59]. The desired immobilized a-hydroxy esters can be obtained by microwave-mediated ring opening of the corresponding glycidyl esters by OH-, NH-, or SH-terminal polystyrenes of the Merri-... 

Oxazolin-2-ones 88 are formed when a-hydroxyamides 85) (R, R = alkyl or aiyl) are treated with the cumulated phosphorus ylide 86. The reactions are thought to proceed via the intermediates 87 <97LA217>. The diazomalonylurea derivative 89 is converted into the betaine 91 in the presence of a catalytic amount of dirhodium tetraacetate, presumably by way of the rhodium complex 90 (L = ligand). The betaine reaiTanges to the isomiinchnone 92, which reacts... 

Multicomponent reactions of phosphines, diynedioates, and aryl aldehydes provided tri-substituted furans appending reactive phosphorus ylides, through cumulated trienoates as key intermediates (140L5792). 

The allyl vinyl ether 93, which was obtained via Wittig olefination between a-hy-droxy allyl ester 92 and cumulated phosphorus ylide, was thermally converted to Z- and T-isomers 96 by heating the solutions [69, 70]. 

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