The regioselectivity of the hydrosilylation of substituted 1,3-dienes catalysed by several rhodium complexes in the presence and absence of oxygen was studied. In addition to the already known accelerating effect, the presence of oxygen strongly affected the product distribution. For 2-substituted 1,3-dienes in the presence of oxygen the regioselectivity was in the range of 1 ∶ 6 to 1 ∶ 10 in favour of the head-product, while the absence of oxygen changed the ratios to 1 ∶ 1 to 3 ∶ 1 in favour of the tail-product. When HSiPh3 was used in the presence of oxygen a single isomer was isolated in 87% yield, while in the absence of oxygen a mixture of products was produced. Control experiments indicated that a heterogeneous/colloidal catalytic system may be responsible for the preferred head-product formation.
{"title":"The effect of oxygen on the regioselectivity in the rhodium catalysed hydrosilylation of 1,3-dienes","authors":"M. Gustafsson, T. Frejd","doi":"10.1039/B106143G","DOIUrl":"https://doi.org/10.1039/B106143G","url":null,"abstract":"The regioselectivity of the hydrosilylation of substituted 1,3-dienes catalysed by several rhodium complexes in the presence and absence of oxygen was studied. In addition to the already known accelerating effect, the presence of oxygen strongly affected the product distribution. For 2-substituted 1,3-dienes in the presence of oxygen the regioselectivity was in the range of 1 ∶ 6 to 1 ∶ 10 in favour of the head-product, while the absence of oxygen changed the ratios to 1 ∶ 1 to 3 ∶ 1 in favour of the tail-product. When HSiPh3 was used in the presence of oxygen a single isomer was isolated in 87% yield, while in the absence of oxygen a mixture of products was produced. Control experiments indicated that a heterogeneous/colloidal catalytic system may be responsible for the preferred head-product formation.","PeriodicalId":17260,"journal":{"name":"Journal of the Chemical Society, Perkin Transactions 2","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2002-12-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"79074084","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
A. L. Botes, Daniel Harvig, M. S. V. Dyk, I. Sarvary, T. Frejd, M. Katz, B. Hahn‐hägerdal, M. Gorwa-Grauslund
Yeast strains from more than 31 different genera were screened for the enantioselective reduction of bicyclo[2.2.2]octane-2,6-dione (1). Reducing activity was found in 80% of the screened yeasts. Bicyclo[2.2.2]octane-2,6-dione was enantioselectively reduced (>98% ee) to (1R,4S,6S)-6-hydroxybicyclo[2.2.2]octane-2-one (−)-2 by 69% of the strains. Enantioselective reduction of the diketone to (1S,4R,6S)-6-hydroxybicyclo[2.2.2]octane-2-one ((+)-3, >98% ee) as a major product is reported for the first time. Candida tropicalis UOFS Y-0534 and Candida wickerhamii UOFS Y-0652 displayed this unusual diastereoselectivity.
{"title":"Screening of yeast species for the stereo-selective reduction of bicyclo[2.2.2]octane-2,6-dione","authors":"A. L. Botes, Daniel Harvig, M. S. V. Dyk, I. Sarvary, T. Frejd, M. Katz, B. Hahn‐hägerdal, M. Gorwa-Grauslund","doi":"10.1039/B111064K","DOIUrl":"https://doi.org/10.1039/B111064K","url":null,"abstract":"Yeast strains from more than 31 different genera were screened for the enantioselective reduction of bicyclo[2.2.2]octane-2,6-dione (1). Reducing activity was found in 80% of the screened yeasts. Bicyclo[2.2.2]octane-2,6-dione was enantioselectively reduced (>98% ee) to (1R,4S,6S)-6-hydroxybicyclo[2.2.2]octane-2-one (−)-2 by 69% of the strains. Enantioselective reduction of the diketone to (1S,4R,6S)-6-hydroxybicyclo[2.2.2]octane-2-one ((+)-3, >98% ee) as a major product is reported for the first time. Candida tropicalis UOFS Y-0534 and Candida wickerhamii UOFS Y-0652 displayed this unusual diastereoselectivity.","PeriodicalId":17260,"journal":{"name":"Journal of the Chemical Society, Perkin Transactions 2","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2002-04-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"80903845","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
S. Camiolo, Philip A. Gale, M. Ogden, B. Skelton, Allan H. White
Bis-amidinium calix[4]arene receptors were shown to coordinate bis-carboxylate anions in DMSO solution; the crystal structure of the malonate salt of one of the receptors revealed a number of different amidinium–carboxylate interactions, demonstrating the propensity of these species to form complex hydrogen bonding networks.
{"title":"Solid-state and solution studies of bis-carboxylate binding by bis-amidinium calix[4]arenes†","authors":"S. Camiolo, Philip A. Gale, M. Ogden, B. Skelton, Allan H. White","doi":"10.1039/B102831F","DOIUrl":"https://doi.org/10.1039/B102831F","url":null,"abstract":"Bis-amidinium calix[4]arene receptors were shown to coordinate bis-carboxylate anions in DMSO solution; the crystal structure of the malonate salt of one of the receptors revealed a number of different amidinium–carboxylate interactions, demonstrating the propensity of these species to form complex hydrogen bonding networks.","PeriodicalId":17260,"journal":{"name":"Journal of the Chemical Society, Perkin Transactions 2","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2001-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"73776442","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Under strongly acidic conditions, the title compound 1 readily participates in several possible rearrangement pathways, affording a product distribution which is relative to the choice of solvent and acid catalyst. Thus, using chloroform or acetone as the solvents and HBr or HClO4 as the catalysts, compounds 2–4 have been isolated and fully characterised; in addition, compound 5 was identified in the reaction mixture and characterised by 1H NMR spectroscopy. The reaction kinetics of the transformations have been studied by 1H NMR spectroscopy, using deuterated chloroform or acetone as the NMR solvents. A key intermediate in the reaction mechanisms is the allylic carbocation 6, which rearranges to give the fused system 3; in the presence of bromide anions, the carbocation forms an ion-pair intermediate 7, leading to the formation of compounds 2, 4 and/or 5, depending on the solvent.
{"title":"The acid-catalysed rearrangements of 4,5-bis(2-thienylhydroxymethyl)-1,3-dithiole-2-thione","authors":"I. Serebryakov, P. Skabara, I. F. Perepichka","doi":"10.1039/A901178A","DOIUrl":"https://doi.org/10.1039/A901178A","url":null,"abstract":"Under strongly acidic conditions, the title compound 1 readily participates in several possible rearrangement pathways, affording a product distribution which is relative to the choice of solvent and acid catalyst. Thus, using chloroform or acetone as the solvents and HBr or HClO4 as the catalysts, compounds 2–4 have been isolated and fully characterised; in addition, compound 5 was identified in the reaction mixture and characterised by 1H NMR spectroscopy. The reaction kinetics of the transformations have been studied by 1H NMR spectroscopy, using deuterated chloroform or acetone as the NMR solvents. A key intermediate in the reaction mechanisms is the allylic carbocation 6, which rearranges to give the fused system 3; in the presence of bromide anions, the carbocation forms an ion-pair intermediate 7, leading to the formation of compounds 2, 4 and/or 5, depending on the solvent.","PeriodicalId":17260,"journal":{"name":"Journal of the Chemical Society, Perkin Transactions 2","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"1999-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"78390027","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
1,3,5-Tri[2,6]pyridina-6,9,12-trioxacyclododecaphane-2,4-dione, C21H17N3O7, crystallizes in space group A2/a with a= 20.124(6), b= 12.194(3), c= 15.385(2)A, β= 92.13(2)°, and Z= 8. Refinement using 1 882 diffractometer-measured data yields R 0.038. The corresponding 2,4-bis(ethylenedioxy)-1,3,5-tri[2,6]pyridina-6,9,12-trioxacyclododecaphane, C25H25N3O7, crystallizes in space group P21/c with a= 10.454(4), b= 27.144(7), c= 9.168(3)A, β= 115.09(2)°, and Z= 4. Refinement based upon 2 173 diffractometer-measured data yields R 0.054. The conformation of the diacetal macrocycle is globular; the main backbone of the molecule wraps around a central cavity in a shape somewhat like the seam of a tennis ball. The diketone molecule exhibits a much more open conformation. In both molecules, the linkage of the polyether chain to the pyridine ring is essentially cis to the nitrogen atom. A partial localization of double bonds of the asymmetrically substituted pyridine rings of both structures is noted.
{"title":"The crystal structures of a ketone and related acetal macrocycle containing 2,6-pyridino and polyether subunits","authors":"F. Fronczek, S. Watkins, G. Newkome","doi":"10.1039/P29810000877","DOIUrl":"https://doi.org/10.1039/P29810000877","url":null,"abstract":"1,3,5-Tri[2,6]pyridina-6,9,12-trioxacyclododecaphane-2,4-dione, C21H17N3O7, crystallizes in space group A2/a with a= 20.124(6), b= 12.194(3), c= 15.385(2)A, β= 92.13(2)°, and Z= 8. Refinement using 1 882 diffractometer-measured data yields R 0.038. The corresponding 2,4-bis(ethylenedioxy)-1,3,5-tri[2,6]pyridina-6,9,12-trioxacyclododecaphane, C25H25N3O7, crystallizes in space group P21/c with a= 10.454(4), b= 27.144(7), c= 9.168(3)A, β= 115.09(2)°, and Z= 4. Refinement based upon 2 173 diffractometer-measured data yields R 0.054. The conformation of the diacetal macrocycle is globular; the main backbone of the molecule wraps around a central cavity in a shape somewhat like the seam of a tennis ball. The diketone molecule exhibits a much more open conformation. In both molecules, the linkage of the polyether chain to the pyridine ring is essentially cis to the nitrogen atom. A partial localization of double bonds of the asymmetrically substituted pyridine rings of both structures is noted.","PeriodicalId":17260,"journal":{"name":"Journal of the Chemical Society, Perkin Transactions 2","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"1981-09-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"80767413","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
京公网安备 11010802042870号
京ICP备2023020795号-1
扫码关注我们
求助内容：
应助结果提醒方式：