The Experts below are selected from a list of 5235 Experts worldwide ranked by ideXlab platform
Hisashi Yamamoto - One of the best experts on this subject based on the ideXlab platform.
-
Ketone Super Silyl Enol Ethers in Sequential Reactions: Diastereoselective Generation of Tertiary Carbinols in One Pot
Journal of the American Chemical Society, 2008Co-Authors: Matthew B. Boxer, Matsujiro Akakura, Hisashi YamamotoAbstract:Ketone super Silyl Enol Ethers are shown to be excellent nucleophiles in the Mukaiyama aldol reaction as well as in sequential one-pot diastereoselective reactions. High yields and diastereoselectivities are obtained with a variety of Silyl Enol Ether/aldehyde/Grignard combinations. The utility of this reaction is exemplified in a one-pot 4-component reaction generating two secondary and one tertiary alcohol in one step.
-
Triflimide (HNTf2)-catalyzed aldehyde cross-aldol reaction using "super Silyl" Enol Ethers.
Nature protocols, 2006Co-Authors: Matthew B. Boxer, Hisashi YamamotoAbstract:The synthesis of the acetaldehyde-derived tris(trimethylSilyl)Silyl (super Silyl) Enol Ether is described, as well as its use in the high-yielding aldehyde cross-aldol reaction. The super Silyl Enol Ether shows unprecedented reactivity in giving the 1:1 adduct in very high yield. This reaction is catalyzed by 0.05 mol% of the Bronsted acid triflimide (HNTf2) and is complete within 15 min, making the protocol very attractive for large-scale synthesis.
Scott D. Rychnovsky - One of the best experts on this subject based on the ideXlab platform.
-
Silyl Enol Ether Prins Cyclization: Diastereoselective Formation of Substituted Tetrahydropyran-4-ones
2016Co-Authors: Gidget C. Tay, Chloe Y Huang, Scott D. RychnovskyAbstract:ABSTRACT: A diastereoselective synthesis of cis-2,6-disubstituted tetrahydropyran-4-ones was developed. The key step of this methodology, a Silyl Enol Ether Prins cyclization, was promoted by a condensation reaction between a hydroxy Silyl Enol Ether and an aldehyde to afford substituted tetrahydropyran-4-ones. The cyclization was tolerant of many functional groups, and the modular synthesis of the hydroxy Silyl Enol Ether allowed for the formation of more than 30 new tetrahydropyran-4-ones with up to 97 % yield and>95:5 dr. The cyclization step forms new carbon−carbon and carbon−oxygen bonds, as well as a quaternary center with good diastereoselectivity. The method provides a versatile route for the synthesis of substituted tetrahydropyrans. Substituted tetrahydropyrans and tetrahydropyranones are a common motif in numerous biologically active natural products (Figure 1).1 Synthesis of tetrahydropyran-4-ones (THPOs), followed by reduction of the ketone, has been used to form 4
-
Silyl Enol Ether Prins Cyclization: Diastereoselective Formation of Substituted Tetrahydropyran-4-ones
2015Co-Authors: Gidget C. Tay, Chloe Y Huang, Scott D. RychnovskyAbstract:A diastereoselective synthesis of cis-2,6-disubstituted tetrahydropyran-4-ones was developed. The key step of this methodology, a Silyl Enol Ether Prins cyclization, was promoted by a condensation reaction between a hydroxy Silyl Enol Ether and an aldehyde to afford substituted tetrahydropyran-4-ones. The cyclization was tolerant of many functional groups, and the modular synthesis of the hydroxy Silyl Enol Ether allowed for the formation of more than 30 new tetrahydropyran-4-ones with up to 97% yield and >95:5 dr. The cyclization step forms new carbon–carbon and carbon–oxygen bonds, as well as a quaternary center with good diastereoselectivity. The method provides a versatile route for the synthesis of substituted tetrahydropyrans
-
Silyl Enol Ether prins cyclization diastereoselective formation of substituted tetrahydropyran 4 ones
Journal of Organic Chemistry, 2014Co-Authors: Chloe Y Huang, Scott D. RychnovskyAbstract:A diastereoselective synthesis of cis-2,6-disubstituted tetrahydropyran-4-ones was developed. The key step of this methodology, a Silyl Enol Ether Prins cyclization, was promoted by a condensation reaction between a hydroxy Silyl Enol Ether and an aldehyde to afford substituted tetrahydropyran-4-ones. The cyclization was tolerant of many functional groups, and the modular synthesis of the hydroxy Silyl Enol Ether allowed for the formation of more than 30 new tetrahydropyran-4-ones with up to 97% yield and >95:5 dr. The cyclization step forms new carbon–carbon and carbon–oxygen bonds, as well as a quaternary center with good diastereoselectivity. The method provides a versatile route for the synthesis of substituted tetrahydropyrans.
Kenneth Hanson - One of the best experts on this subject based on the ideXlab platform.
-
enantioselective protonation of Silyl Enol Ether using excited state proton transfer dyes
Organic Letters, 2016Co-Authors: Suliman Ayad, Kenneth HansonAbstract:Enantiopure excited state proton transfer (ESPT) dyes were used for the asymmetric protonation of Silyl Enol Ether. Under 365 nm irradiation, with 3,3′-dibromo-VANOL as the ESPT dye, up to 49% enantioselectivity with a 68% yield of product was observed at room temperature. The reaction is effective with a range of Silyl Enol Ethers and can also be achieved with visible light upon the addition of triplet sensitizer. The relatively low ee of the protonated product is due to the racemization/decomposition of the ESPT dye in the excited state as indicated by circular dichroism, HPLC, and UV–vis spectroscopy.
-
Enantioselective Protonation of Silyl Enol Ether Using Excited State Proton Transfer Dyes
2016Co-Authors: Anjan Das, Suliman Ayad, Kenneth HansonAbstract:Enantiopure excited state proton transfer (ESPT) dyes were used for the asymmetric protonation of Silyl Enol Ether. Under 365 nm irradiation, with 3,3′-dibromo-VANOL as the ESPT dye, up to 49% enantioselectivity with a 68% yield of product was observed at room temperature. The reaction is effective with a range of Silyl Enol Ethers and can also be achieved with visible light upon the addition of triplet sensitizer. The relatively low ee of the protonated product is due to the racemization/decomposition of the ESPT dye in the excited state as indicated by circular dichroism, HPLC, and UV–vis spectroscopy
Toshinobu Higashimura - One of the best experts on this subject based on the ideXlab platform.
-
multifunctional coupling agents for living cationic polymerization 7 synthesis of amphiphilic tetraarmed star block polymers with α methylstyrene and 2 hydroxyethyl vinyl Ether segments by coupling reactions with tetrafunctional Silyl Enol Ether
Macromolecules, 1996Co-Authors: Hiroji Fukui, Mitsuo Sawamoto, Saiko Yoshihashi, Toshinobu HigashimuraAbstract:By the polymer coupling reaction with a tetrafunctional Silyl Enol Ether [1; C{CH2OC6H4C(OSiMe3)CH2}4], amphiphilic tetraarmed star polymers (6) with α-methylstyrene−2-hydroxyethyl vinyl Ether (αMeSt−HOVE) block arm chains have been synthesized: C{CH2OC6H4COCH2−[CH(OCH2CH2OH)CH2]n−[C(CH3)(C6H5)CH2]m−}4. The synthesis consisted of the following steps: (i) the sequential living cationic polymerization of αMeSt and 2-[(tert-butyldimethylSilyl)oxy]ethyl vinyl Ether (SiVE) into an αMeSt−SiVE living block copolymer (4); (ii) the coupling of four chains of 4 with the quencher 1 into a tetraarmed polymer (5); and (iii) the transformation of the poly(SiVE) segment into the poly(HOVE) chain by the fluoride-catalyzed deprotection. In step i the living polymerization was carried out at −78 °C in methylene chloride with a binary initiating system comprising tin tetrabromide and the hydrogen chloride adduct of 2-chloroethyl vinyl Ether. After step iii, the tetraarmed amphiphile 6 (αMeSt/HOVE = 27/27 in n in each arm)...
-
multifunctional coupling agents for living cationic polymerization 5 synthesis of amphiphilic tetraarmed star poly vinyl Ethers by coupling reactions with tetrafunctional Silyl Enol Ether
Macromolecules, 1995Co-Authors: Hiroji Fukui, Mitsuo Sawamoto, Toshinobu HigashimuraAbstract:Amphiphilic tetraarmed star poly(vinyl Ethers), where each arm carries alkyl (hydrophobic) and alcohol (hydrophilic) pendant groups, have been synthesized by the coupling reaction of AB-block living poly(vinyl Ethers) (4; arm chain) with a tetrafunctional Silyl Enol Ether 1, C[CH 2 OC 6 H 4 -p-C(OSiMe 3 )=CH 2 ] 4 . The living arm chaise 4 were prepared by the sequential living cationic polymerization of an alkyl vinyl Ether (CH 2 =CHOR 1 ; R 1 =iBu, CH 2 CH 2 Cl) and a fuctionalized vinyl Ether (CH 2 =HOCH 2 -CH 2 R 2 ; R 2 =OCOCH 3 , OSi t BuMe 2 ) with hydrogen chloride/zinc chloride initiating system in methylene chloride at -15 o C. The treatment of 4 with the Silyl Enol Ether 1 led to tetraarmed block copolyiners 5. The yield of 5 (93-73%) depended on the structure and the polymerization sequence of the monomer pair for the arm chain 4. The best result (93% yield) was obtained with the AB-block polymer of 2-chloroethyl vinyl Ether (R 1 =CH 2 CH 2 Cl; CEVE) and 2-acetoxyethyl vinyl Ether (R 2 =OCOCH 3 ; AcOVE) where CEVE has polymerized first. Separate coupling experiments with the homopolymers of these vinyl Ethers showed that the coupling yield was higher for monomers with less bulky pendant groups. Subsequent quantitative deprotections of the acetoxy of tert-butyldimethylSilyl groups in 5 into hydroxyl groups gave the amphiphilic tetraarmed polymers 6. By changing the polymerization sequence of the monomer pair, the hydrophilic polyalcohol segments could be placed either inside or outside the tetraarmed structure. For pairs of such inner- and outer-alcohol versions with identical segmental compositions, solubility and arm-chain conformation (by 1 H NMR) were compared
Stephen Rimmer - One of the best experts on this subject based on the ideXlab platform.
-
synthesis of oligo isobutyl vinyl Ether with a Silyl Enol Ether end group and their aldol reactions with benzaldehyde
Macromolecular Chemistry and Physics, 2005Co-Authors: Prodip Sarker, Stephen RimmerAbstract:Cationic polymerizations of isobutyl vinyl Ether (iBVE) were carried out in the presence of a difunctional Silyl Enol Ether, 3,3-dimethylpent-2,4-(trimethylSilyloxy)-1,4-diene. This procedure gave oligomers with Silyl Enol Ether end groups. The Silyl Enol Ether groups reacted in Lewis acid mediated aldol reactions with benzaldehyde to give predominately the β-hydroxy ketone product at the chain end. Benzaldehyde could be added either prior to initiation (ab initio methodology) or at a time after the propagation of iBVE had completed (sequential methodology). The ah initio methodology was shown to produce similar materials to the sequential method but the latter required higher reaction temperatures.
-
Cationic polymerization of vinyl Ethers in the presence of Silyl Enol Ethers
Macromolecular Chemistry and Physics, 2004Co-Authors: Weihong Lang, Prodip Sarker, Stephen RimmerAbstract:Vinyl Ether oligomers with reactive end groups were prepared by alkylation of Silyl Enol Ethers during propagation. Silyl Enol Ethers were added to the cationic polymerization of isobutyl vinyl Ether, ethyl vinyl Ether and methyl vinyl Ether. The polymerization were carried out under non-living conditions so that, in the absence of added Silyl Enol Ether, MALDI TOF mass spectrometry gave evidence for end groups other than those derived from reaction with the methanol capping agent. Addition of either phenyl-1-(trimethylSilyloxy)ethylene or 1-methoxyphenyl-1-(trimethylSilyloxy)ethylene significantly reduced the fraction of end groups derived from intramolecular termination reactions, such as elimination, at temperatures between 21 and -78°C. However, as in living systems lowering the reaction temperature increased the proportion of chains with the desired chain-end functionality (i.e. aryl ketone derived from alkylation of the Silyl Enol Ether). α-β Elimination also produced a population of isobutyl vinyl Ether oligomers with α-β unsaturated ketone end groups.
-
synthesis of telechelic oligo isobutyl vinyl Ether s via alkylation of Silyl Enol Ethers by the propagating chain end in an ab initio cationic polymerisation
Macromolecular Rapid Communications, 2001Co-Authors: Weihong Lang, Stephen RimmerAbstract:Telechelic oligomers prepared by cationic polymerisation of isobutyl vinyl Ether were synthesised by an ab initio procedure, in which Silyl Enol Ethers were alkylated by the propagating carbocationic chain end. In-situ addition of a Silyl Enol Ether to the propagating chain end in a cationic polymerisation yields functionalized oligomers during the polymerisation. Therefore, it is not necessary to operate under living conditions.