- Cobalt-Catalyzed Allylic C(sp3)-H Carboxylation with CO2
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Catalytic carboxylation of the allylic C(sp3)-H bond of terminal alkenes with CO2 was developed with the aid of a Co/Xantphos complex. A wide range of allylarenes and 1,4-dienes were successfully transformed into the linear styrylacetic acid and hexa-3,5-dienoic acid derivatives in moderate to high yields, with excellent regioselectivity. The carboxylation showed remarkable functional group tolerability, so that selective addition to CO2 occurred in the presence of other carbonyl groups such as amide, ester, and ketone. Since styrylacetic acid derivatives can be readily converted into optically active γ-butyrolactones through Sharpless asymmetric dihydroxylation, this allylic C(sp3)-H carboxylation showcases a facile synthesis of γ-butyrolactones from simple allylarenes via short steps.
- Michigami, Kenichi,Mita, Tsuyoshi,Sato, Yoshihiro
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supporting information
p. 6094 - 6097
(2017/05/08)
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- Synthesis of the AB-ring pyranolactone substructure of granaticin A
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A synthesis of the AB-ring substructure of granaticin A was developed. The pyranolactone moiety was stereoselectively accessed by Sharpless asymmetric dihydroxylation and subsequent oxa-Pictet-Spengler cyclization. The use of BF3·OEt2 resulted in the formation of the cis pyranolactone, whereas the combination of BF3·OEt2 with trifluoroacetic acid led to the trans isomer. The resulting hydroquinones were cleaved selectively by ozonolysis to dicarboxylic acids. An aryl Grignard reagent could be regioselectively added to unsymmetrical anhydrides. As an alternative strategy for the construction of the B-ring, a benzyne-furan cycloaddition could be established. Synthesis of the AB-ring substructure of granaticin A was accomplished. The pyranolactone moiety was stereoselectively accessed by Sharpless asymmetric dihydroxylation and oxa-Pictet-Spengler cyclization. Ozonolysis of a hydroquinone led to pyranolactone anhydrides. Regioselective addition of a Grignard reagent to an unsymmetrical anhydride was observed. An alternative strategy was also investigated. Copyright
- Bartholomaeus, Ruben,Bachmann, Janina,Mang, Christian,Haustedt, Lars Ole,Harms, Klaus,Koert, Ulrich
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p. 180 - 190
(2013/02/23)
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- Synthesis of isochroman-3-ylacetates and isochromane-γ-lactones through rearrangement of aryldioxolanylacetates
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Lewis acid catalysed rearrangement of methyl 4,5-trans-4-aryldioxolan-5-ylacetates 1 provides a convenient route to substituted methyl isochroman-3-ylacetates 2 and isochromane-γ-lactones 3. The choice of Lewis acid is determined by the substitution pattern of the aromatic ring. The two contiguous isochromane stereocentres are transferred unchanged from the parent dioxolanes, while the configuration of the isochromane methyl group is dependent upon the aryl substitution, the reagent and the reaction conditions. Thus treatment of the C-2 epimeric 3′,5′-dimethoxyphenyldioxolanes 4 and 5 with camphorsulfonic acid afforded a mixture of the C-5 epimeric isochromane lactones 26 and 29, the former being favoured at lower acid concentrations, the latter at higher concentrations. Titanium tetrachloride isomerised the analogous 2′-chloro-5′-methoxyphenyldioxolanes 6 and 7 into the methyl isochroman-3-ylacetate 38, which could be lactonised to the isochromane lactone 27. Phosphoric acid converted the 2′,5′-dimethoxyphenyldioxolanes 8 and 9 into a mixture of the isochromane lactones 28 and 31, while similar treatment of the hydroxylactone 22 in the presence of acetaldehyde afforded the isochromane lactone 28 directly and with complete diastereoselectivity. Oxidative demethylation and annulation of this isochromahe lactone 28 afforded 5-epi-7-deoxykalafungin 41.
- Giles, Robin G. F.,Rickards, Rodney W.,Senanayake, Badra S.
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p. 3949 - 3956
(2007/10/03)
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- Reaction of 2-Butenoic Acid Dianion and Its N-(4-Methoxyphenyl)amide with Methoxy-Substituted Arynes
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N-(4-Methoxyphenyl)-1-butenamide dianion (6), generated by the reaction of N-(4-methoxyphenyl)-2-butenamide (3) with LDA or LTMP, undergoes exclusive 4-arylation with various methoxy-substituted arynes 2a-e yielding mixtures consisting of a N-(4-methoxyphenyl)-(E)-4-aryl-3-butenamide (9) (85-90percent) and a N-(4-methoxyphenyl)-(E)-4-aryl-2-butenamide 9' (10-15percent).Under certain conditions, 4,4-diarylated products 12 are also obtained. 2-Butenoic acid dianion (14) also reacts with methoxy-substituted arynes affording predominantly 4-aryl-3-butenoic acids 15 and minor amountsof 4-aryl-2-butenoic acids 15'.The exclusive low temperature (-30 to -40 deg C) 4-addition of arynes to dianion 14 is in contrast to the predominant 2-addition that 14 undergoes with certain aldehydes and ketones at comparable temperatures.The mixtures of 4-arylbutenoic acids 15 and 15' and 4-arylbutenamides 9 and 9' were readily hydrogenated (Pd/C) and esterified (MeOH/H2SO4) to synthetically valuable methyl 4-arylbutanoates 17.
- Deshmukh, Abdul Rakeeb,Tran, Long,Biehl, Edward R.
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p. 667 - 670
(2007/10/02)
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