- Trifluoroacetic anhydride - Catalyzed conjugate addition of boronic acids to α,β-unsaturated ketones
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The conjugate addition of boronic acids to α,β-unsaturated ketones catalyzed by acylating reagents has been explored. The results show that trifluoroacetic anhydride catalyzes the addition of vinylboronic acids under experimentally simple and metal-free conditions for a variety of substrates with good yields.
- Roscales, Silvia,Rincón, ángela,Buxaderas, Eduardo,Csák?, Aurelio G.
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experimental part
p. 4721 - 4724
(2012/09/08)
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- Products and mechanism of the reaction of chlorine atoms with 3-pentanone in 700-950 Torr of N2/O2 diluent at 297-515 K
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The products, kinetics, and mechanism of the reaction Cl + 3-pentanone have been measured by UV irradiation of Cl2/3-pentanone/N2 (O2) mixtures using primarily GC analysis with selected cross checks by FTIR. In the absence of O2, the products are 1- and 2-chloro-3-pentanone with yields of 21 and 78%, respectively. As the temperature is increased, the yield of 1-chloro-3-pentanone increases modestly relative to the 2-chloro-3-pentanone yield. On the basis of this increase, the activation energy for hydrogen abstraction at the 1 position is determined to be 500 (±500) cal mole-1 relative to abstraction at the 2 position. In the presence of 500 ppm of O2 with 900-1000 ppm of Cl2 at 297 K, the yield of 2-chloro- 3-pentanone decreases dramatically from 78 to 2.5%, while the 1-chloro-3-pentanone decreases only modestly from 21 to 17%. The observed oxygenated species are acetaldehyde (59%), 2,3-pentanedione (9%), and propionyl chloride (56%). Increasing the temperature to 420 K (O2 = 500 ppm) suppresses these oxygenated products, and 2-chloro-3-pentanone again becomes the primary product, indicating that the O2 addition reaction to the 2-pentanonyl radical has become reversible. At 500 K and 10 000 ppm O 2, a new product channel opens which forms a small yield (~4%) of ethylvinylketone. Computer modeling of the product yields has been performed to gain an understanding of the overall reaction mechanism in the presence and absence of O2. The reaction of chlorine atoms with 3-pentanone proceeds with a rate constant of 8.1 (±0.8) × 10-11 cm3 molecule-1 s-1 independent of temperature over the range of 297-490 K (Ea = 0 ± 200 cal mole-1). Rate constant ratios of K(C2H 5C(O)CHCH3 + Cl2)/ k(C2H 5C(O)CHCH3 + O2) = 0.0185 ± 0.0037 and k(C2H5C(O)CH2CH + Cl2)/ k(C 2H5CH2C(O)CH2CH2 + O 2) = 2.7 ± 0.4 were determined at 297 K in 800-950 Torr of N2/O2 diluent. In 800-950 Torr of N2/O 2 diluent, the major fate of the alkoxy radical CH 3CH(O)C(O)C2H5 is decomposition to give C 2H5C(O) radicals and CH3CHO. These results show that the chemical mechanisms of the 3-pentanone reactions are very similar to those observed for butanone. In addition, the rate constants of the reactions of chlorine atoms with 1-chloro-3-pentanone [3 (±0.6) x 10-11 over the range of 297-460 K], 2,3-pentanedione [1.4 (±0.3) × 10-11 at 297 K], and ethylvinylketone [1.9 (±0.4) × 10-10 over the range of 297-400 K, decreasing rapidly above 400 K] were measured at ambient pressure.
- Kaiser,Wallington,Hurley
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experimental part
p. 343 - 354
(2010/06/15)
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- An expedient, flexible and convergent access to selectively protected 1,5-dicarbonyl compounds. Applications to the synthesis of 2,6-disubstituted pyridines and thiopyridines
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Intermolecular addition of 2-oxoalkyl radicals generated from the corresponding S-alkyl-O-ethyl dithiocarbonates on vinyl ketals afforded selectively protected 1,5-dicarbonyl compounds in good yields. These key-intermediates can be converted into a plethora of useful substances. Transformations to pyridines and thiopyridines were given as examples. Georg Thieme Verlag Stuttgart.
- Boivin, Jean,Carpentier, Floriane,Jrad, Rafik
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p. 1664 - 1672
(2007/10/03)
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- First Stereoselective Synthesis of (1S,2S,4R,5R)-(-)-β-Multistriatin
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Starting from 2,3-O-(3-pentylidene)-D-glyceraldehyde (3), we prepared the bicyclic pheromone (1S,2S,4R,5R)-(-)-β-multistriatin (1) on a gram scale.Key steps of the synthesis are a cis-selective Wittig olefination followed by diastereoselective Michael addition and hydrogenation. - Key Words: Multistriatin / 2,3-O-(3-Pentylidene)-D-glyceraldehyde / Wittig Olefination, cis-selective / Michael reaction, diastereoselective / Hydrogenation, diastereoselective
- Henrichfreise, Peter,Scharf, Hans-Dieter
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p. 1011 - 1014
(2007/10/02)
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- A Synthetic Approach to the Quassinoids
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A synthetic route to the quassinoids has been developed.Two-stage annelation of 2-methylcyclohexanone with 1-chloro-3-pentanone gives tricyclic dienone 9 (60percent), which is oxidized by acetyl chromate in acetic acid to give dienedione 27 (80percent).Bisketalization of this material followed by hydrolysis of the conjugated enone ketals provides monoketal 30 (77percent), along with recovered 27.Ring C of 30 is functionalized by the Stiles and Reich methods to obtain the unsaturated keto ester 33 (73percent).The latter material reacts with ketene acetal 35 at 5-6 kbar and room temperature to give an adduct that is desilylated by treatment with aqueous KF; keto diester 39 is produced in 95percent yield.Epoxidation of 39 occurs smoothly with m-CPBA to give 46 (88percent), which is converted into allylic alcohol 40 by the two-step Sharpless procedure (78percent).Finally, pyridinium chlorochromate induces solvolytic cyclization of 40, affording 41 in 55percent yield.In the course of the investigation, it was also discovered that β-keto ester 46 is oxidized by m-CPBA to 47 in quantitative yield.
- Heathcock, Clayton H.,Mahaim, Cyril,Schlecht, Matthew F.,Utawanit, Thanin
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p. 3264 - 3274
(2007/10/02)
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- N-(Heterocycl ic-alkyl)-9-xanthenylamines
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The compounds are N-(imidazolylalkyl, imidazolinylalkyl and tetrahydropyrimidylalkyl)-9-xanthenylamines which have gastric acid secretion inhibitory activity.
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