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Carbon-oxygen bonds cyclizations

Mesoxalates are highly reactive substrates because of their strongly polarized carbon-oxygen bond. They have been used in pericyclic processes (e.g. Diels-Alder reactions,8 ene reactions,9 [3+2]10 and [2+2]11 cycloadditions), in aldol12 and Wittig as well as Friedel-Crafts reactions.13 Further applications arise from the use of the corresponding imines in hetero Diels-Alder reactions14 and electrophilic cyclizations.15... [Pg.109]

The environmentally benign synthesis of lactones has attracted attention because of their importance in natural product chemistry. The oxidative cyclization of diols via carbon-oxygen bond formation is the most well-known approach for the synthesis of lactones [70]. [Pg.135]

The thermally induced cyclization of A -(benzyloxycarbonyl)phenyl ketenimines 415, obtained in a two-step, one-pot procedure from benzyl 2-azidobenzoates 414, led to 2-substituted-4/f-3,l-benzoxazin-4-ones 416 (Scheme 79). The reaction involves the formation of a new carbon-oxygen bond and migration of the benzyl group from the oxygen atom to the terminal carbon atom of the ketenimine fragment <2005S2426>. [Pg.428]

A rather more complex tertracyclic indole based compound lowers blood pressure by selective blockade of a 1-adrenergic receptors. Reaction of the anion from indole (72-1) with butyrolactone (72-2) leads to the scission of the carbon-oxygen bond in the reagent and the formation of the alkylated product (72-3). The acid is then cyclized onto the adjacent 2 position to give the ketone (72-4) by treatment with a Lewis acid such as polyphosphoric acid. Reaction with bromine then leads to the brominated ketone (72-5). This is subjected to reductive alkylation with ethylene... [Pg.624]

Cu(hfacac)2-catalyzed elimination of N2 from aroyl(a-diazoacyl)hydra-zines 653 yields 2//-l,3,4-oxadiazin-2-ones 654 (70%). The reaction occurs consecutively via intramolecular carbonyl ylide formation, 1,3-cyclization into oxirane 655, and ring opening by the carbon-oxygen bond followed by a C- 0 shift with ring expansion (88CB887). [Pg.196]

Several cyclization approaches to afford oxadiazine substructures have been reported via a carbon-oxygen bond-formation step. In the examples presented here, at least one sp carbon is present in the ring, which is involved in a double bond in either endo- or exocyclic fashion. Several examples where the oxadiazine moiety is a part of a polycyclic system are presented in this chapter. [Pg.486]

After insertion of the palladium into the carbon-oxygen bond of the trienyl triflate 120, the (S)-BINAP (2,2 -bis(diphenylphosphinyl)-l,l -binaphthalene) ligand on the palladium led to selective coordination to one of the enantiotopic double bonds with subsequent cyclization to give the intermediate tt-allyl complex 124. This was regio- and stereoselectively trapped by the nucleophile. Further elaboration of 121 gave the natural product with good optical purity. [Pg.571]

Interestingly, however, despite changes in cation and solvent, it is often stereochemical demands that dictate the product formed. For example, in the intramolecular cyclizations shown in Scheme 9.87,treatmentof5-bromo-3,3-dimethyl-2-pentanone with lithium diisopropylamide ([(CH3)2C]2N LT, LDA) in ether results in O-alkylation with the formation of 2-methylene-3,3-dimethyloxacyclopentane (2-methylene-3,3-dimethyltetrahydrofuran), despite the fact that carbon-oxygen bonds tend to be shorter (141 pm) than carbon-carbon bonds (154pm). On the other hand, the analogous 6-bromo-3,3-dimethyl-2-hexanone, under the same reaction conditions, produces 2,2-dimethylcyclohexanone. [Pg.836]

The transformation of enantiomerically enriched 1,1,4-trisubstituted but-2-yne-l,4-diols (262) into 2,2,5-trisubstituted 3-acyloxy-2,5-dihydrofurans (267) with complete stereospecificity has been achieved by an Ag(I)-mediated rearrangement of the monoesters (263) to allenic intermediates (265), followed by Ag(I)-assisted cycUzation. A possible mechanism for the rearrangement and cyclization is shown in Scheme 66, in which the carbon-oxygen bond (b) in (266) is formed from the back side of the carbon-oxygen bond (a) in (264). A novel synthetic method has been developed for the rearrangement of 3-aryl-l,2-dialkynylallyl alcohols into m-enediynes under mild acidic conditions. The allylic rearrangement has been shown to involve an acid-catalysed isomerization step to convert the allyl alcohol into an allylic cation... [Pg.615]

In the year 2010, the group of Danishefsky reported the first asymmetric total synthesis of (-)-phalarine by using a Mannich reaction/Wagner-Meerwein rearrange-ment/cyclization cascade sequence (Scheme 13.9) [10], In this reaction cascade, one carbon-nitrogen bond, one carbon-carbon bond, one carbon-oxygen bond, and two new rings were formed. [Pg.373]

The synthetic strategy utilized by Still and coworkers, detailed in Scheme 37, contained two aspects unique within the macrocyclic trichothecene field. First, the macrocycle was constructed by a carbon-carbon bond forming reaction (299- 300) in contrast to the usual cyclization by way of a carbon-oxygen bond. Second, additional chiral centers were introduced onto an already formed macrocycle. Previous endeavors had accounted for all the chiral centers prior to their incorporation into the... [Pg.207]

For recent reviews, see (a) Hartung, J., Gottwald, T, and Spehar, K., Selectivity in the chemistry of oxygen-centered radicals the formation of carbon-oxygen bonds. Synthesis, 1469, 2002 (b) Hartung, J., Stereoselective construction of the tetrahydrofuran nucleus by alkoxyl radical cyclizations, Eur. J. Org. Chem., 619, 2001. [Pg.1354]

Motta A, Fragala IL, Marks TJ (2010) Atom-efficient carbon-oxygen bond formation processes. DPT analysis of the intramolecular hydroalkoxylation/cyclization of alkynyl alcohols mediated by lanthanide catalysts. Organometallics 29 2004—2012... [Pg.49]

In accord with an a f/-parallel relationship between the migrating carbon (C20) and the entering nucleophile, the carbon chlorine bond in 364-Cl is found to be in the equatorial (a) configuration. On the other hand, the acid-catalyzed cyclization of methyl betulonate (367), and related diol occurs so as to form an axial carbon-oxygen bond to C19, despite the ostensibly unfavorable stereoelectronics 453, 454). It is possible, however, that this transformation is more complex than a simple ring expansion followed by lactonization. [Pg.193]


See other pages where Carbon-oxygen bonds cyclizations is mentioned: [Pg.350]    [Pg.815]    [Pg.319]    [Pg.128]    [Pg.1072]    [Pg.20]    [Pg.507]    [Pg.166]    [Pg.9]    [Pg.1072]    [Pg.191]    [Pg.73]    [Pg.367]    [Pg.20]    [Pg.153]    [Pg.413]    [Pg.413]    [Pg.592]    [Pg.122]    [Pg.1594]    [Pg.4]    [Pg.59]    [Pg.138]    [Pg.267]    [Pg.141]    [Pg.231]    [Pg.261]    [Pg.1594]    [Pg.106]    [Pg.272]    [Pg.413]    [Pg.1323]    [Pg.382]   
See also in sourсe #XX -- [ Pg.815 , Pg.816 , Pg.817 ]




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Carbon oxygenated

Carbon oxygenation

Carbon-oxygen bond

Carbonates cyclization

Cyclization oxygenative

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