ABSTRACT ChemInform is a weekly Abstracting Service, delivering concise information at a glance t... more ABSTRACT ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.
ABSTRACT ChemInform is a weekly Abstracting Service, delivering concise information at a glance t... more ABSTRACT ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.
ABSTRACT ChemInform is a weekly Abstracting Service, delivering concise information at a glance t... more ABSTRACT ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.
Botryodiplodin and (±)-epi-botryodiplodin acetates were prepared in good yields following a pract... more Botryodiplodin and (±)-epi-botryodiplodin acetates were prepared in good yields following a practical four step route. The method, for the construction of the strategic tetrahydrofuran ring, hinged on an unprecedented halogen atom transfer Ueno-Stork cyclization of an O-allyl a,a-dihalohemiacetal acetate, catalyzed by the redox complex CuCl/N,N,N 0 ,N 00 ,N 00pentamethyldiethylenetriamine.
ABSTRACT ChemInform is a weekly Abstracting Service, delivering concise information at a glance t... more ABSTRACT ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.
Application of 1,3-Azomethine Ylides Derived from α-Dicarbonyl Compounds and L-Proline to the Syn... more Application of 1,3-Azomethine Ylides Derived from α-Dicarbonyl Compounds and L-Proline to the Synthesis of Pyrrolizidines.-The one-pot three-component reaction between diacetyl compounds (I), β-nitrostyrene (II), and L-proline (III) in isopropanol at room temperature affords the regioisomeric cycloadducts (IV) and (V). In contrast, the cycloadduct (XI) is formed from cyclohexanedione (X) only when the reaction is performed in refluxing isopropanol. At room temperature incorporation of the amine component into the products fails and bicyclooctanones (XII) and (XIII) are the result of a tandem Michael-Henry reaction. In this case L-proline acts as a catalyst, although with modest enantioselectivity. In order to determine the mechanism of formation of the pyrrolizidines, a reaction is performed between butanedione (Ia), (II), and hydroxyproline (VI), thus taking advantage of the presence of a stereocenter of known configuration.
The natural fragrances (+)-trans whisky lactone 2 and (+)-trans cognac lactone 4, together with a... more The natural fragrances (+)-trans whisky lactone 2 and (+)-trans cognac lactone 4, together with a minor amount of their (À)cis stereoisomers, were prepared in 50% and 42% overall yield, respectively, starting from racemic 1-hepten-3-ol (±)-5 and 1-octen-3-ol (±)-6. The procedure involved first the enantioconvergent, lipase mediated transformation of the secondary allylic alcohols derived dichloroacetates (±)-7 and (±)-8 into the corresponding homochiral (+)-7 and (+)-8, combined with their cyclization under a transition metal catalyzed atom transfer process.
Enantiopure (99% ee) cis-and trans-c-benzylparaconic acids and their ethyl esters were synthesize... more Enantiopure (99% ee) cis-and trans-c-benzylparaconic acids and their ethyl esters were synthesized by a procedure involving kinetic enzymatic resolution of the corresponding lactonic esters with a-chymotrypsin (a-CT) with acetone added as a cosolvent. Their absolute configurations were determined by 1 H NMR analysis of their 1-(9-anthryl)-2,2,2-trifluoroethyl esters.
Paraconic acid 4, (S)-())-terebic acid 6 and their corresponding methyl and ethyl esters having e... more Paraconic acid 4, (S)-())-terebic acid 6 and their corresponding methyl and ethyl esters having eeÕs ranging from 60% to 92% were obtained by enzymatic resolution of their racemates. The enzymatic resolution of racemic ethyl c-methylparaconates 14a and 14b allowed the isolation of the unreacted ester (2R,3R)-(+)-14a and that of the lactonic acid (2S,3R)-())-5b with 80% and 93% ee, respectively, the former by the use of Horse liver acetone powder (HLAP), the latter using a-chymotrypsin (a-CT). The enantiomeric ethyl (2S,3S)-())-14a and (2S,3R)-())-14b, both with >99% ee, were obtained by bakerÕs yeast reduction of diethyl acetylsuccinate.
The formation of enantiopure d-lactones condensed with alicyclic rings has been achieved either b... more The formation of enantiopure d-lactones condensed with alicyclic rings has been achieved either by reduction with baker's yeast of the corresponding d-keto esters and d-keto acids or by enzymic resolution of the former compounds. The absolute con®gurations of the lactones were determined by means of CD spectroscopy, using the correlation method.
Both enantiomers of the diastereomeric cognac lactones have been synthesised using enzyme assiste... more Both enantiomers of the diastereomeric cognac lactones have been synthesised using enzyme assisted reactions in the enantiodifferentiating step. This was accomplished by baker's yeast reduction of their precursors 3-methyl-4-oxononanoic acid and ester and by enzymatic hydrolysis of the latter. An inhibition of hydrolases by the products was observed. Trans-(+)-, trans-(−)-, cis-(+)-and cis-(−)-cognac lactones having 99, 88, 88 and 99% e.e., respectively, were thus obtained. Their CD spectra have also been studied.
Enantiomerically pure condensed δ-lactones have been prepared from the corresponding δ-ketoesters... more Enantiomerically pure condensed δ-lactones have been prepared from the corresponding δ-ketoesters by the use of Saccharomyces cerevisiae. The reactions were not only highly enantioselective but also highly diastereoselective, provided the baker's yeast was preincubated at 50°C for 30 min. Interestingly, and contrary to what is usually found, the use of nutrients inhibited the bioreductions. The relative configurational assignments have been made by means of NMR, while the absolute configurations and conformations of the lactone rings were attributed by means of CD studies.
The CD curves of a set of condensed y-butyrolactones have been investigated. A simple correlation... more The CD curves of a set of condensed y-butyrolactones have been investigated. A simple correlation between the sign of the Cotton effect (CE) and the configuration of Ca can be deduced from the resulting data.
ABSTRACT ChemInform is a weekly Abstracting Service, delivering concise information at a glance t... more ABSTRACT ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.
ABSTRACT ChemInform is a weekly Abstracting Service, delivering concise information at a glance t... more ABSTRACT ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.
ABSTRACT ChemInform is a weekly Abstracting Service, delivering concise information at a glance t... more ABSTRACT ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.
Botryodiplodin and (±)-epi-botryodiplodin acetates were prepared in good yields following a pract... more Botryodiplodin and (±)-epi-botryodiplodin acetates were prepared in good yields following a practical four step route. The method, for the construction of the strategic tetrahydrofuran ring, hinged on an unprecedented halogen atom transfer Ueno-Stork cyclization of an O-allyl a,a-dihalohemiacetal acetate, catalyzed by the redox complex CuCl/N,N,N 0 ,N 00 ,N 00pentamethyldiethylenetriamine.
ABSTRACT ChemInform is a weekly Abstracting Service, delivering concise information at a glance t... more ABSTRACT ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.
Application of 1,3-Azomethine Ylides Derived from α-Dicarbonyl Compounds and L-Proline to the Syn... more Application of 1,3-Azomethine Ylides Derived from α-Dicarbonyl Compounds and L-Proline to the Synthesis of Pyrrolizidines.-The one-pot three-component reaction between diacetyl compounds (I), β-nitrostyrene (II), and L-proline (III) in isopropanol at room temperature affords the regioisomeric cycloadducts (IV) and (V). In contrast, the cycloadduct (XI) is formed from cyclohexanedione (X) only when the reaction is performed in refluxing isopropanol. At room temperature incorporation of the amine component into the products fails and bicyclooctanones (XII) and (XIII) are the result of a tandem Michael-Henry reaction. In this case L-proline acts as a catalyst, although with modest enantioselectivity. In order to determine the mechanism of formation of the pyrrolizidines, a reaction is performed between butanedione (Ia), (II), and hydroxyproline (VI), thus taking advantage of the presence of a stereocenter of known configuration.
The natural fragrances (+)-trans whisky lactone 2 and (+)-trans cognac lactone 4, together with a... more The natural fragrances (+)-trans whisky lactone 2 and (+)-trans cognac lactone 4, together with a minor amount of their (À)cis stereoisomers, were prepared in 50% and 42% overall yield, respectively, starting from racemic 1-hepten-3-ol (±)-5 and 1-octen-3-ol (±)-6. The procedure involved first the enantioconvergent, lipase mediated transformation of the secondary allylic alcohols derived dichloroacetates (±)-7 and (±)-8 into the corresponding homochiral (+)-7 and (+)-8, combined with their cyclization under a transition metal catalyzed atom transfer process.
Enantiopure (99% ee) cis-and trans-c-benzylparaconic acids and their ethyl esters were synthesize... more Enantiopure (99% ee) cis-and trans-c-benzylparaconic acids and their ethyl esters were synthesized by a procedure involving kinetic enzymatic resolution of the corresponding lactonic esters with a-chymotrypsin (a-CT) with acetone added as a cosolvent. Their absolute configurations were determined by 1 H NMR analysis of their 1-(9-anthryl)-2,2,2-trifluoroethyl esters.
Paraconic acid 4, (S)-())-terebic acid 6 and their corresponding methyl and ethyl esters having e... more Paraconic acid 4, (S)-())-terebic acid 6 and their corresponding methyl and ethyl esters having eeÕs ranging from 60% to 92% were obtained by enzymatic resolution of their racemates. The enzymatic resolution of racemic ethyl c-methylparaconates 14a and 14b allowed the isolation of the unreacted ester (2R,3R)-(+)-14a and that of the lactonic acid (2S,3R)-())-5b with 80% and 93% ee, respectively, the former by the use of Horse liver acetone powder (HLAP), the latter using a-chymotrypsin (a-CT). The enantiomeric ethyl (2S,3S)-())-14a and (2S,3R)-())-14b, both with >99% ee, were obtained by bakerÕs yeast reduction of diethyl acetylsuccinate.
The formation of enantiopure d-lactones condensed with alicyclic rings has been achieved either b... more The formation of enantiopure d-lactones condensed with alicyclic rings has been achieved either by reduction with baker's yeast of the corresponding d-keto esters and d-keto acids or by enzymic resolution of the former compounds. The absolute con®gurations of the lactones were determined by means of CD spectroscopy, using the correlation method.
Both enantiomers of the diastereomeric cognac lactones have been synthesised using enzyme assiste... more Both enantiomers of the diastereomeric cognac lactones have been synthesised using enzyme assisted reactions in the enantiodifferentiating step. This was accomplished by baker's yeast reduction of their precursors 3-methyl-4-oxononanoic acid and ester and by enzymatic hydrolysis of the latter. An inhibition of hydrolases by the products was observed. Trans-(+)-, trans-(−)-, cis-(+)-and cis-(−)-cognac lactones having 99, 88, 88 and 99% e.e., respectively, were thus obtained. Their CD spectra have also been studied.
Enantiomerically pure condensed δ-lactones have been prepared from the corresponding δ-ketoesters... more Enantiomerically pure condensed δ-lactones have been prepared from the corresponding δ-ketoesters by the use of Saccharomyces cerevisiae. The reactions were not only highly enantioselective but also highly diastereoselective, provided the baker's yeast was preincubated at 50°C for 30 min. Interestingly, and contrary to what is usually found, the use of nutrients inhibited the bioreductions. The relative configurational assignments have been made by means of NMR, while the absolute configurations and conformations of the lactone rings were attributed by means of CD studies.
The CD curves of a set of condensed y-butyrolactones have been investigated. A simple correlation... more The CD curves of a set of condensed y-butyrolactones have been investigated. A simple correlation between the sign of the Cotton effect (CE) and the configuration of Ca can be deduced from the resulting data.
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