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Wittig reaction vinylogous

The vinylogous nitroso-substituted TTF 807 was obtained in the Wittig reaction of the phosphonium salt 800 with the aldehyde 806. The second nitroso group in 807 was introduced by nitrosation using isoamyl nitrite to give 808 (Scheme 122) <1997JOC2616>. [Pg.1051]

Because of its enhanced reactivity, diethoxyvinylidenetriphenylphosphorane adds a variety of CH acids, even those which do not react with 0x0-, thioxo- and imino-vinylidenetriphenylphosphorane. Irreversible loss of ethanol from the initially formed Michael adduct gives phosphoranes which are vinylogs of 3-keto ylides if the starting material is an acidic carbonyl compound (equation lOS). CH-acidic carbonyl compounds also may add to diethoxyvinylidenetriphenylphosphorane via the enolate oxygen, thus leading to orthoester phosphoranes which can undergo intramolecular Wittig reaction. ... [Pg.193]

Another chiral vinylogous urethane, 677, played a central role in the synthesis of (- )-652 by Lhommet and co-workers (Scheme 90) 494). This compound, prepared from (/ )-a-methylbenzylamine (678) (495), was diastereoselectively hydrogenated over platinum oxide to give the amino-ester 679 (de >95%). More significantly, methylation of the anion of 679 under conditions of kinetic control afforded 680 (de ca 98%) in 33% overall yield from the chiral amine 496). Wittig reaction of the aldehyde derivative 681 with the stabilized ylide l-(triphenylphosphoranylidene)-2-heptanone yielded 682 (90%) as a 4 1 mixture of E and Z isomers. When this product... [Pg.198]

A new electron donor tetrathiafulvalene vinylogue (240) has been synthesized using both phosphonium ylide- and phosphonate-based olefinations (Scheme 20). 25 Both Wittig reactions and Wadsworth-Emmons reactions have also been applied to the synthesis of new vinylogous tetrathiafulvalenes, e.g. (243). from (241) and (242). 26... [Pg.349]

Meyers and co-workers have continued their studies to exploit the synthetic potential of a-lithio-formamidines and have now described an efficient synthesis of 2-aryl- or 2-heteroaryl-pyrrolidines and -piperidines (266 ). " Alkylation of formamidines (264) gives intermediates (265) which cyclize in situ after cleavage of the amidine unit. The aza-Wittig reaction has been utilized in a general synthesis of heterocyclic vinylogous ure-thanes and amides (268). Staudinger reaction of azides (267)... [Pg.512]

Paquette et al. start with the bis-vinylogation of the same compound 29 [14], by Wittig-Horner reaction, reduction, and oxidation (Scheme 5). For the formation of the C17-C16 bond, the onti-aldol 41 (ds not reported) is obtained by treatment of the aldehyde 39 with the (Z)-boron enolate 40, bearing a dithioketal moiety that is later to be the C51-C54 side chain. 3-Hydroxy-assisted, diastereoselective reduction of the keto group at C15 gives 41, which is converted into intermediate 42 in five more steps. The dethioketalization of 41 is achieved with phenyliodine(m) bis(trifluoroacetate) [16], As in Nicolaou s synthesis, the N12-C13 amide bond is formed first, followed by a low-yielding (21%, even at a concentration of 1 him) macrolactonization to 3. Table 1 summarizes the benchmark data of the two total syntheses of sanglifehrin A (1). [Pg.357]

Synthesis. We envisioned the key step in the synthesis of vinylogous lactones of formula 5 to be formation of the exocyclic double bond via a Wittig-type reaction. [Pg.93]


See other pages where Wittig reaction vinylogous is mentioned: [Pg.42]    [Pg.344]    [Pg.365]    [Pg.42]    [Pg.344]    [Pg.365]    [Pg.551]    [Pg.239]    [Pg.42]    [Pg.303]    [Pg.451]    [Pg.55]    [Pg.1137]    [Pg.765]    [Pg.765]    [Pg.190]    [Pg.88]    [Pg.62]    [Pg.765]    [Pg.156]    [Pg.193]    [Pg.190]    [Pg.17]    [Pg.487]    [Pg.249]    [Pg.14]    [Pg.791]    [Pg.791]    [Pg.28]    [Pg.691]    [Pg.261]    [Pg.689]    [Pg.791]    [Pg.585]   
See also in sourсe #XX -- [ Pg.344 , Pg.365 ]




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