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Orthoesters, vinyl

Polymerization Catalyst. Several types of polymerization have been promoted by trityl fluoroborate, including reactions of orthocarbonates and orthoesters, vinyl ethers, epoxides, and lactones... [Pg.437]

Elimination of two equivalents of ROH after condensation between an allyl alcohol and an orthoester will provide the allyl vinyl ether which undergoes the [3,3]-sigmatropic rearrangement. [Pg.154]

The study of the cleavage of the axial and the equatorial vinyl bicyclic orthoesters HO and H (Fig. 10) with potassium permanganate was reported recently (1, 3). Permanganate reacts with the vinyl orthoester double-bond yielding first 142 and then the tetrahedral intermediate 143. On that basis,... [Pg.53]

The permanganate oxidation of axial and equatorial vinyl orthoesters 140 and 141 was carried out in a buffered solution (pH =10) mixed with acetonitrile. The reaction mixture was then esterified with acetic anhydride and pyridine. Both vinyl orthoesters gave an identical result >95% of acetoxy ester J46 and <5% of bicyclic lactone 147. [Pg.54]

Hydrolysis of cyclic orthoesters Ozonolysis of tetrahydropyranyl ethers Cleavage of vinyl orthoesters... [Pg.201]

In previous studies, i,e. concurrent carbonyl-oxygen exchange in the hydrolysis of esters, acid hydrolysis of orthoesters and oxidation of acetals by ozone, the configuration of the tetrahedral intermediate was determined by the application of the principle of stereoelectronic control. There could be some ambiguity in these experiments as the theory of stereoelectronic control is used to predict both the stereochemistry of the tetrahedral intermediate as well as its breakdown. The oxidation cleavage of vinyl orthoesters can therefore be considered a more powerful experimental technique in that respect because the configuration of the hemi-orthoester... [Pg.248]

Similar to cell attachment, endosomal escape of simple lamellar complexes is a process driven by electrostatics [21, 25, 83] (see Sect. 2) and therefore inhibited by PEGylation. A strategy to recover efficient endosomal escape is to prepare PEG-lipids in which the PEG chains are attached via bonds that are quickly cleaved as the endosomal pH is lowered in the course of maturation. This practically converts the shielded complex back into an unshielded complex. Several acid-labile moieties have been investigated for similar purposes, e.g., hydrazones [92], vinyl ethers [93] and orthoesters [87, 94]. [Pg.220]

In order to circumvent such a drawback, there has been a recent focus on the design of cleavable lipids whose hydrolysis is catalyzed by the drop in pH.10 This approach exploits acid-labile chemical groups such as acetals, ketals, orthoesters, and vinyl ethers. Such functional groups... [Pg.363]

CLy -Enals and -enones.17 The TiCl4-catalyzed reaction of lithium trialkyl(l-al-kynyl)borates with methyl vinyl ketone (10, 402) has been extended to a similar reaction with orthoesters, which results in allylic boranes that are oxidized to a,p-enones and -ei als (equation I). [Pg.499]

A mercury-free route to allyl vinyl ethers that relies on the Michael addition of allyl alcohols to unsubstituted alkenyl sulfoxides, followed by thermal loss of sulfenic acid and concurrent Claisen rearrangement has been described [145]. This methodology has been applied to the synthesis of isocar-bacyclin [146]. Posner reported an acid-catalyzed protocol that produces conjugated dienoate esters from allylic alcohols and a sulfinyl orthoester [147]. Additionally, the use of propargyl alcoholates and a chloro alkenyl sulfox-... [Pg.121]

Scheme 51 presents an entirely different mode of catalyzed [4 + 2] cycloadditions. Thus irimediylsilyl triflate or triflic acid apparently transform vinyl orthoesters and acrolein acetals to powerful transient allyl cation dienophiles (214) and (219), respectively. The ionic Diels-Alder reactions (213) (216)... [Pg.341]

Whereas Eschenmoser and Johnson variants of the Claisen rearrangement utilize an excess of amide acetal and orthoester precursors, respectively, for generation of the vinyl ether functionality, the Carroll... [Pg.831]

This chapter focuses the attention on the reactions of nonstabilized carbanionic compounds such as alkyl, vinyl, aryl, alkynyl metals, etc., and the chemistry of the stabilized system, i.e. allylic, propargylic or oxaallylic carbanions is presented in Volume 2 of this series. Electrophiles with C=X bonite which are discussed include aldehydes, ketones, epoxides, aziridines, acetals, orthoesters and imines, all of which turn into highly reactive electrophiles in the presence of Lewis acids. [Pg.326]

The synthesis of a-selenoalkyl metals reported above is not limited to those compounds which possess alkyl or aryl groups on an sp carbanionic center. For example, a-selenoalkyllithiums bearing a vinyl (Scheme 94), furfuryl (Scheme 95), silyl (Scheme 96), - methoxy (Scheme 97) or seleno moiety (Schemes 77 and 98) 7t have been obtained in alinost quantitative yield from the corresponding fimctionalized selenoacetals - or orthoesters and Bu Li. The Se-Li exchange is in all these cases, except that of tris(phenylseleno)methane, exclusively observed even with those compounds which possess a hydrogen susceptible to metallation. The 6,6-bis(phenylseleno)-p-lactam shown... [Pg.664]

The total synthesis of apoptolidin was accomplished in the laboratory of K.C. Nicolaou. The key C12-C28 vinyl iodide fragment was prepared using the Schwartz hydrozirconation of an internal alkyne followed by trapping of the alkenylzirconium intermediate with iodine (I2). The vinyl iodide was formed as a 6 1 mixture of regioisomers. Under the reaction conditions, the methyl orthoester was converted to the methyl glycoside moiety at C21, which was presumably facilitated by the complexation of Zr with the pyranoside oxygen atom. [Pg.401]

CH2 -C(OMe)NMe2 in DMF for 24 hr at 160 C.233 Hydroxyesters can be made from furfural cyanohydrin and when heated with an orthoester afford vinyl ethers that rearrange in a similar manner (Scheme 58).234 The ester substituent appears to promote the rearrangement by stabilizing the intermediate. [Pg.297]


See other pages where Orthoesters, vinyl is mentioned: [Pg.247]    [Pg.451]    [Pg.152]    [Pg.53]    [Pg.54]    [Pg.248]    [Pg.432]    [Pg.37]    [Pg.152]    [Pg.78]    [Pg.46]    [Pg.160]    [Pg.88]    [Pg.499]    [Pg.46]    [Pg.397]    [Pg.209]    [Pg.273]    [Pg.532]    [Pg.615]    [Pg.167]    [Pg.673]    [Pg.160]    [Pg.451]   


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Orthoester

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