- Intramolecular Reaction of (γ-Alkoxyallyl)stannane with Aldehyde: Origin of the Stereoselectivities
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The intramolecular cyclization of simple acyclic (γ-alkoxyallyl)stannane aldehydes 1, 2, and 12-15 was investigated to elucidate the relationship between the geometry of the double bond of the allylstannanes, the ring size of cyclic ethers produced by the cyclization, and the procedures for promoting the cyclization. The Lewis acid-mediated cyclization of 1-2, 12-13, and 14-15 gave the trans cyclic ethers 3, 39, and 41, respectively, either predominantly or exclusively irrespective of the geometry of the double bond and of the ring size of the cyclic ethers. The relationship in the thermal cyclization of 1 and 2, which gave the 6-membered cyclic ethers 4 and 3, was straightforward; the Z isomer 1 gave the cis product 4, and the E isomer 2 afforded the trans product 3. However, the relationship in the thermal cyclization of 12 and 13 which afforded the 5-membered cyclic ethers 39 and 40 was different from that expected from the cyclization via the well-accepted cyclic transition state, as observed in the case of 1 and 2. Both the Z (12) and E (13) isomers gave the cis cyclic ether 40 either predominantly or exclusively. The protic acid-mediated (or -catalyzed) cyclization of 12-13 and 14-15 gave the trans cyclic ethers 39 and 41, respectively, regardless of the geometry of the double bonds. On the other hand, the protic acid-promoted cyclization of 1 and 2 was very strange; the Z isomer 1 gave the cis isomer 4, and the E isomer 2 afforded the trans isomer 3. The mechanisms for these cyclization reactions are proposed.
- Kadota, Isao,Kawada, Miho,Gevorgyan, Vladimir,Yamamoto, Yoshinori
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- Intramolecular [4 + 3] cycloadditions - Stereochemical issues in the cycloaddition reactions of cyclopentenyl cations - A synthesis of (+)-dactylol
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Five cyclopentanones were prepared for the purpose of examining the effects of stereogenic centers on the course of the intramolecular [4 + 3] cycloaddition reactions of cyclopentenyl cations. One substrate reacted with very high levels of diastereoselect
- Harmata, Michael,Rashatasakhon, Paitoon,Barnes, Charles L.
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- Facile and selective deprotection of PMB ethers and esters using oxalyl chloride
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Oxalyl chloride, (0.5 equiv) was found to cleave the PMB group from alkyl, aryl PMB ethers, and esters to give corresponding alcohol and acid in good yields. This method offers simple and efficient protocol for the selective deprotection of PMB ether and ester in DCE at ambient temperature.
- Ilangovan, Andivelu,Anandhan, Karnambaram,Kaushik, Mahabir Prasad
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p. 1081 - 1084
(2015/02/19)
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- A convenient approach for the deprotection and scavenging of the PMB group using POCl3
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A convenient and high yielding approach for the deprotection and scavenging of the p-methoxybenzyl (PMB) group in PMB ethers and PMB esters was developed using POCl3 as the reagent. 4-Methoxybenzyl chloride, a starting material used for the preparation of PMB ethers and esters was regenerated in the deprotection step. This mild and selective procedure tolerates several acid sensitive functional groups. The Royal Society of Chemistry 2013.
- Ilangovan, Andivelu,Saravanakumar, Shanmugasundar,Malayappasamy, Subramani,Manickam, Govindaswamy
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p. 14814 - 14828
(2013/09/02)
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- Efficient medium ring size bromolactonization using a sulfur-based zwitterionic organocatalyst
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Catalytic bromolactonization of long-chain olefinic acids resulting in the efficient synthesis of medium-sized lactones is reported using a zwitterionic catalyst and stoichiometric N-bromosuccinimide halogen source. The reaction was found to be more efficient at 0 °C than at room temperature, which could be attributed to the temperature dependence of the zwitterionic catalyst.
- Cheng, Yi An,Chen, Tao,Tan, Chong Kiat,Heng, Jun Jie,Yeung, Ying-Yeung
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supporting information
p. 16492 - 16495,4
(2020/09/15)
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- Element having porphyrin polymer fixed on a substrate and method of preparing the same
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A photo-functional molecule element having, on a substrate, a porphyrin polymer containing covalently-fixed porphyrin units, and the method of preparing the same. The photo-functional molecule element may be used as a photoelectric conversion element such as an organic solar cell or a three-dimensional, non-linear organic material.
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- Process for producing allyl-containing compounds
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An allyl-containing compound represented by following Formula (3): wherein R2, R3, R4, R5 and R6 may be the same as or different from one another and each represent hydrogen atom or an organic group; R7 represents an organic group; and Y represents oxygen atom or sulfur atom, is produced by reacting an allyl ester compound represented by following Formula (1): wherein R1 represents hydrogen atom or an organic group; and R2, R3, R4, R5 and R6 are as defined above, with a compound represented by following Formula (2):R7-Y-H wherein R7 is an organic group; and Y is as defined above, in the presence of at least one transition element compound.
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- A mild and efficient selective tetrahydropyranylation of primary alcohols and deprotection of THP ethers of phenols and alcohols using PdCl 2(CH3CN)2 as catalyst
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Primary alcohols were selectively tetrahydropyranylated in good to excellent yields at room temperature using PdCl2(CH 3CN)2 as catalyst in tetrahydrofuran (THF) in the presence of phenols, secondary, and tertiary alcohols. The tetrahydropyranyl (THP) group could be efficiently removed using PdCl2(CH 3CN)2 as catalyst in CH3CN, while other protection groups such as p-toluenesulfonyl (Ts), tert-butyldiphenylsilyl (TBDPS), benzyloxycarbonyl (Cbz), allyl, benzyl (Bn), and benzoyl (Bz) remained intact under these conditions.
- Wang, Yan-Guang,Wu, Xiao-Xing,Jiang, Zhi-Yong
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p. 2973 - 2976
(2007/10/03)
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- A facile zirconium(IV) chloride catalysed selective deprotection of t-butyldimethylsilyl (TBDMS) ethers
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A simple and efficient protocol for the selective deprotection of t-butyldimethylsilyl (TBDMS) ethers using 20 mol% ZrCl4 in 20-45 min and in high yields, is reported, wherein it is demonstrated that acid and base sensitive groups and allylic and benzylic groups are unaffected.
- Sharma,Srinivas,Radha Krishna, Palakodety
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p. 4689 - 4691
(2007/10/03)
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- Deprotection of tetrahydropyranyl ethers with montmorillonite K-10 clay in methanol
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A variety of tetrahydropyranyl (THP) ethers are removed by Montmorillonite K-10 clay in methanol at room temperature to give alcohols. It has been shown that the THP ethers carrying epoxy, methoxymethoxy (MOMO), tertbutyldiphenylsiloxy (TBDP-SO-), acetoxy (AcO-) and benzoyloxy (BzO-) functionalities are stable under the conditions, while the ethers carrying ketal, tertbutyldimethylsioxy (TBSO-) and β,β,β-trichloroethylimidoxy [CCl3C(=NH)O-] functionalities are unstable.
- Taniguchi, Takahiko,Kadota, Kohei,Elazab, Adel S.,Ogasawara, Kunio
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p. 1247 - 1248
(2007/10/03)
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- Hydrocarbonylation of prop-2-en-1-ol to butane-1,4-diol and 2-methylpropan-1-ol catalysed by rhodium triethylphosphine complexes
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The hydrocarbonylation of prop-2-ene-1-ol catalysed by [Rh2(O2CMe)4]-PEt3, which gives [RhH(CO)(PEt3)2] as the active species, has been found to produce predominantly butane-1,4-diol and 2-methylpropan-1-ol with small amounts of 2-methylpropane-1,3-diol and propan-1-ol. Neither 2-methylprop-2-enal nor 2-methylprop-2-en-1-ol are intermediates in the production of 2-methylpropan-1-ol. By carrying out the reaction under a variety of reaction conditions and by using deuterium-labelling studies it was possible to formulate a mechanism for the production of 2-methylpropan-1-ol which involves formation of the vinyl alcohol, 2-methylprop-1-en-1-ol, as the primary product followed by tautomerism and hydrogenation, provided that at least two PEt3 groups are co-ordinated to the rhodium. A dehydration is proposed to occur during the catalytic cycle from a cationic hydroxycarbene intermediate. Using propenyl ethers as substrates similar products are obtained presumably via loss of alcohol rather than dehydration. If less than two PEt3 groups are co-ordinated to rhodium the major branched-chain product from prop-2-en-1-ol is 2-methylpropane-1,3-diol. This is interpreted as indicating that protonation of the acyl intermediate and dehydration of the hydroxycarbene do not occur because of the lower electron density on the acyl O atom.
- Simpson, Michael C.,Currie, Alan W. S.,Andersen, Jo-Ann M.,Cole-Hamilton, David J.,Green, Michael J.
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p. 1793 - 1800
(2007/10/03)
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- Synthesis of novel mimetics of the sialyl Lewis X determinant
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Mimetics of the sialyl Lewis-X determinant in which at least one sugar domain is simulated by a di-, tri- or tetraalcohol unit have been synthesized. The inhibitory potency of these compounds for E- and P-selectin mediated cell adhesion has been evaluated in cell culture assays. The receptor binding affinity of the best of these mimetics was slightly higher than that of the natural oligosaccharide ligand sialyl Lewis X.
- Toepfer,Toepfer, Alexander,Kretzschmar,Kretzschmar, Gerhard,Bartnik,Bartnik, Eckart
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p. 9161 - 9164
(2007/10/02)
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- New acyclic analogues of lipid A: synthesis of 4-phosphonoxybutyl and 3-phosphonoxypropyl glycosides of 2-amino-2-deoxy-D-glucose
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Several analogues of lipid A have been synthesized, in which the reducing monosaccharide moiety of the parent molecule has been replaced by an acyclic spacer.The new compounds show high endotoxic activity and are able to protect neutropenic mice against pseudomonas infection, two properties characteristic of LPS-like molecules.
- Eustache, Jacques,Grob, Alfred,Retscher, Hannelore
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p. 251 - 268
(2007/10/02)
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- Asymmetric epoxidation of allyl alcohol derivatives by ω-hydroxylase from Pseudomonas oleovorans
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This paper described the application of non-heme monooxygenase system from Pseudomonas oleovorans to the syntheses of chiral 3-(benzyloxy)-, 3-(allyloxy)-, 3-(butyloxy)- and 3-(aryloxy)-1,2-epoxypropanes (6) from their corresponding allyl alcohol derivatives.The epoxides were determined to be R forms with good enantiomeric excess.The specificities of the enzymatic epoxidation of olefines and hydroxylation of the radical probe trans-2-phenyl-1-methylcyclopropane were discussed with regard to the reaction mechanism.
- Fu, Hong,Shen, Gwo-Jenn,Wong, Chi-Huey
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p. 167 - 170
(2007/10/02)
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- Autoxidation of Allyl Ether Compounds. Part 1. Reactivity of Allyl Ether Alcohols.
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Cobalt catalyzed liquid phase autoxidations of some primary and secondary allyl ether alcohols were studied at 30 and 40 deg C.An optimum concentration for the catalyst was found, above which cobalt behaved like an inhibitor.Autoxidations of secondary allyl ether alcohols started immediately after adding the catalyst but the reactions of the allyl ethers of primary diols were preceded by induction periods.Induction periods depended on the carbon chain length of the diol and were not observed after methylating the hydroxyl group of the allyl ether alcohol.The phenomena are explained as resulting from inter- and intramolecular hydrogen bonding, which controls the autoxidation by decreasing the electron density on the etheral oxygen.
- Toivonen, Hannu
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