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Lactones seven-membered

The lactone concept is not restricted to the simple model biaryl synthesis presented here. It has been successfully expanded to a broad series of structurally diverse biaryl substrates (e.g., lactones with additional stereocenters and functional groups, configurationally stable lactones, seven-membered lactones, and again configurationally unstable biaryl hydroxy aldehydes ), to different activation modes in the ring-opening step (e.g., use of metallated nucleophiles, carbonyl activation by Lewis acids, (Ti -complexation, etc.), and for various strategies of stereoselection (e.g., external vs. internal asymmetric induction). ... [Pg.187]

Pyrolysis, at 520 °C, of simple macrocyclic lactones (seven-membered or greater) affords high yields of open-chain, oj-unsaturated carboxylic acids a six-membered transition state has been proposed " (Scheme 9). Presumably the high temperature of this reaction precludes its application to more complex substrates. Similar unsaturated acids can be obtained by a novel cleavage of 1-tri-methylsiloxybicyclo[ ,l,0]alkanes using lead(iv) tetra-acetate in acetic acid (Scheme 10). [Pg.72]

The synthesis of five-, six-, and seven-membered cyclic esters or timides uses intramolecular condensations under the same reaction condifions as described for intermolecular reactions. Yields are generally excellent. An example from the colchicine synthesis of E.E. van Ta-melen (1961) is given below. The synthesis of macrocyclic lactones (macrolides) and lactams (n > 8), however, which are of considerable biochemical and pharmacological interest, poses additional problems because of competing intermolecular polymerization reactions (see p. 246ff.). Inconveniently high dilution, which would be necessary to circumvent this side-... [Pg.145]

The 1,6-difunctional hydroxyketone given below contains an octyl chain at the keto group and two chiral centers at C-2 and C-3 (G. Magnusson, 1977). In the first step of the antithesis of this molecule it is best to disconnect the octyl chain and to transform the chiral residue into a cyclic synthon simultaneously. Since we know that ketones can be produced from add derivatives by alkylation (see p. 45ff,), an obvious precursor would be a seven-membered lactone ring, which is opened in synthesis by octyl anion at low temperature. The lactone in turn can be transformed into cis-2,3-dimethyicyclohexanone, which is available by FGI from (2,3-cis)-2,3-dimethylcyclohexanol. The latter can be separated from the commercial ds-trans mixture, e.g. by distillation or chromatography. [Pg.206]

It will be recalled that lactone-derived enol triflate 102 was expected to serve as a substrate for a Murai coupling37 with the mixed cuprate reagent derived from iodo ortho ester 103 (see Scheme 17c). If successful, this C-C bond forming process would accomplish the introduction of the remaining carbon atoms needed for the annulation of the seven-membered D-ring lactone. [Pg.773]

The addition of dibutylcupratc to the a-substituted /1-formyl esters 1 preferentially affords, via chelation control, the cw-disubstituted y-lactone 241. These results are in agreement with those found with a-unsubstituted /1-esters39-41 (vide supra), assuming a seven-membered chelate as transition state of the addition reaction. The diastercosclectivity is somewhat lower with esters 1 as the stereogenic center is one carbon atom further removed from the reaction center and therefore the steric influence of the substituent R1 is less pronounced. [Pg.45]

On treatment with trimethyl(2-propenyl)silane and titanium(IV) chloride, chiral methyl fi-formylcarboxylates give di- and tetra-substituted y-lactones with moderate to good stereoselectivity. Participation of seven-membered ring chelates was suggested65. [Pg.350]

CHMO is known to catalyze a number of enantioselective BV reactions, including the kinetic resolution of certain racemic ketones and desymmetrization of prochiral substrates [84—87]. An example is the desymmetrization of 4-methylcyclohexanone, which affords the (S)-configurated seven-membered lactone with 98% ee [84,87]. Of course, many ketones fail to react with acceptable levels of enantioselectivity, or are not even accepted by the enzyme. [Pg.50]

Various cyclic esters have been subjected to hpase-catalyzed ring-opening polymerization. Lipase catalyzed the ring-opening polymerization of 4- to 17-membered non-substituted lactones.In 1993, it was first demonstrated that medium-size lactones, 8-valerolactone (8-VL, six-membered) and e-caprolactone (e-CL, seven-membered), were polymerized by lipases derived from Candida cylindracea, Burkholderia cepacia (lipase BC), Pseudomonas fluorescens (lipase PF), and porcine pancreas (PPL). °... [Pg.207]

The principles set forth above account reasonably well for the course of bifunctional condensations under ordinary conditions and for the relative difficulty of ring formation with units of less than five or more than seven members. They do not explain the formation of cyclic monomers from five-atom units to the total exclusion of linear polymers. Thus 7-hydroxy acids condense exclusively to lactones such as I, 7-amino acids give the lactams II, succinic acid yields the cyclic anhydride III, and ethylene carbonate and ethylene formal occur only in the cyclic forms IV and V. [Pg.99]

Bromomethyl-3,4-dibromo-3,4-dihydrocoumarin 1 (Fig. 11.4) and its chloro-methylated analogue 2b rapidly and progressively inactivate a-chymotrypsin and also the activities of a series of trypsin-like proteases. A benzyl substituent characteristic of good substrates of a-chymotrypsin was introduced at the 3-position to make inhibition more selective. This substituted dihydrocoumarin 3 irreversibly inhibited a-chymotrypsin and other proteases. These functionalized six-membered aromatic lactones, and their five- and seven-membered counterparts, 3//-benzofuran-2-ones 2a26 and 4,5-dihydro-3//-benzo[b]oxepin-2-ones 2c,27 were the first efficient suicide inhibitors of serine proteases. Their postulated mechanism of action is shown in Scheme 11.2. [Pg.363]

Medium-ring acetylenic lactones,2 Cyclization to medium size acetylenic lactones is difficult because of geometric constraint imposed by the triple bond, and has been considered practicable only for at least fifteen-membered rings. Surprisingly, the acetylenic w-hydroxy acid 1 when complexed with Co2(CO), is cyclized in 28% yield to the seven-membered complexed acetylenic lactone 2 by Mukai-yama s reagent, 2-chloro-l-methylpyridinium chloride (8, 95-96). The yield is essentially the same as that observed in lactonizaton to a complexed 10-membered... [Pg.117]

Scheme 16.31 Formation of a seven-membered lactone via Ru-catalyzed cyclocarbonylation. Scheme 16.31 Formation of a seven-membered lactone via Ru-catalyzed cyclocarbonylation.
The use of heterogeneous catalysts in this reaction has also been achieved palladium-montmorillonite clays [93] or palladium/activated carbon [94] in the presence of dppb transformed 2-allylphenols into lactones, the regiose-lectivity of the reaction being largely dependant on the nature of the support. Very recently, palladium complexes immobilized onto silica-supported (polyaminoamido)dendrimers were used as catalysts in the presence of dppb for the cyclocarbonylation of 2-allylphenols, 2-allylanilines, 2-vinylphenols, and 2-vinylanilines affording five-, six-, or seven-membered lactones and lactams. Good conversions are realized and the catalyst can be recycled 3-5 times [95]. [Pg.117]

Caprolactam (5.68, Fig. 5.21) has a seven-membered lactam ring and is a major industrial compound in the production of Nylon , its polymer. This compound shows only moderate levels of toxicity in mice and rats when administered orally. The hydrolysis product 6-aminohexanoic acid (5.69) was a minor metabolite in rats [176]. Hydroxylation in the y-position to yield 5.70 without preliminary hydrolysis of the lactam linkage has been shown to be the major metabolic pathway. This metabolite hydrolyzes in urine to produce 6-amino-4-hydroxyhexanoic acid (5.71), which is in equilibrium with the corresponding lactone (5.72). [Pg.232]

Of great interest is the recent finding that human serum paraoxonase (EC 3.1.8.1, which belongs to the class of A-esterases), is very active in hydrolyzing a range of four-, five-, six-, and seven-membered lactones [167], Some cyclic carbonates (see Sect. 7.6.3) were also substrates. [Pg.422]

When carbon dioxide was used as electrophile, the seven-membered lactone 376 was isolated after treatment of the initially formed hydroxy acid (375 with X = CO2H) with... [Pg.708]

In the case of using carbon dioxide as the electrophile, seven-membered ring lactones were obtained, the reaction being exemplified with compound 405 (67% yield). On the other hand, for carbonyl compound derivatives of type 404, their cyclization under acidic conditions (85% H3PO4, toluene reflux) gave the corresponding cyclic thioethers 406 in 76-90% yield . [Pg.712]

Shibasiki Y, Sanada H, Yokoi M, Sanda F, Endo T (2000) Activated monomer cationic polymerization of lactones and the application to well-defined block copolymer synthesis with seven-membered cyclic carbonate. Macromolecules 33 4316-4320... [Pg.211]

The product is omega-caprolactone, a seven membered lactone that cannot be made by an intramolecular ring closure. [Pg.236]

In the first addition of nitrile ylides to a,()-unsaturated lactones (92), it was found that the reaction of benzonitrilio 4-nitrobenzylide with the lactones 178-180 were strongly regioselective. Compounds 178 and 179 reacted to give [e.g., 181 from 178 (51%)] and its methyl analogue from 179 (54%). The exocyclic double bond in 180 was, however, the most reactive and gave 182 (69%). The six-membered analogue of 178 was less reactive (34%) and the seven-membered analogue failed to react. [Pg.500]

In addition to the examples of diene cyclisations described above there are reports of alkoxyallenes as precursors of five- to seven-membered oxygen heterocycles <99TL1747>. Of interest here is the cyclisation of 45 to 46 in 88% yield in the presence of Pd(0 Ac)2-dppb complex. The same reagent system has also been used in the regioselective lactonisation of steroids where the aromatic ring of estrone is fused to a seven-membered lactone <99TL1171>. [Pg.346]

Lactones with Seven-Membered and Larger Rings... [Pg.779]

In an analogous process polystyrene bound aryl halides, containing a pendant double bond were ring closed, giving the seven membered lacton as the major product (5.7.)7... [Pg.89]


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See also in sourсe #XX -- [ Pg.102 ]




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