- An isomerization-1,3-dipolar cycloaddition tandem reaction towards the synthesis of 3-aryl-4-methyl-5-O-substituted isoxazolines from O-allyl compounds
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A new strategy for the synthesis of 3-aryl-4-methyl-5-O-substituted isoxazolines via tandem catalytic isomerization of O-allyl systems to O-(1-propenyl) systems-1,3-dipolar cycloaddition (1,3-DC) to nitrile oxides is presented. The influence of the heteroatom in Ph-X-CH=CHCH3 (X=O, S, or Se) on the regio- and stereoselectivity of ArCNO 1,3-cycloaddition to these dipolarophiles is analyzed as well. The dipolarophiles were obtained via [RuClH(CO)(PPh3)3]-, [RuH2(CO)(PPh 3)]- or base (KOH/18-crown-6)-catalyzed double bond migration in corresponding allyl ethers, O-allyl acetals, PhS- and PhSe-allyl systems. Cycloadditions of nitrile oxides to O-(1-propenyl) systems were fully regioselective whereas in the reactions of ArCNO with the PhS-(1-propenyl) and PhSe-(1-propenyl) systems both possible regioisomers were formed. It was established that within the majority of dipolarophiles of ROCHCHCH3 type 1,3-DC is concerted, while for some dipolarophiles of RXCH=CHCH3 (X=O and R=Ph3C, 2,3-dihydroxypropyl, tetrahydropyran-2-yl; X=S or Se and R=Ph) type 1,3-DC turns into a two-step reaction with simultaneous rotation about C-C bond. The results of the experiments have been analyzed theoretically using DFT calculations. The results of these calculations agreed well with the experimental data.
- Krompiec, Stanis?aw,Bujak, Piotr,Malarz, Joanna,Krompiec, Micha?,Skórka, ?ukasz,Pluta, Tadeusz,Danikiewicz, Witold,Kania, Magdalena,Kusz, Joachim
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experimental part
p. 6018 - 6031
(2012/09/22)
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- Convenient synthesis of isoxazolines via tandem isomerization of allyl compounds to vinylic derivatives and 1,3-dipolar cycloaddition of nitrile oxides to the vinylic compounds
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A novel effective method for the synthesis of new isoxazolines via tandem isomerization of QCH(X)CH{double bond, long}CH(Y) to QC(X){double bond, long}CHCH2(Y) (Q = RO, RS, R2N, R3Si, etc.; X = H, R, OR; Y = H, R; R = alkyl, aryl) catalyzed by ruthenium complexes and 1,3-dipolar cycloaddition of the latter compounds to arenenitrile oxides is presented. The cycloaddition of QCH(X)CH{double bond, long}CH(Y) to 2,6-dichlorobenzonitrile oxide is also described. The regio- and stereoselectivity of the cycloaddition of nitrile oxide to allyl and 1-propenyl (vinylic in general) compounds is discussed.
- Krompiec, Stanis?aw,Bujak, Piotr,Szczepankiewicz, Wojciech
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supporting information; experimental part
p. 6071 - 6074
(2009/04/11)
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- Relative Thermodynamic Stabilities of Isomeric Alkyl Allyl and Alkyl (Z)-Propenyl Ethers
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The relative thermodynamic stabilities of ten allyl ethers (ROCH2CH=CH2) and the corresponding isomeric (Z)-propenyl ethers (where R is an alkyl group, or a methoxysubstituted alkyl group) have been determined by chemical equilibration in DMSO solution with t-BuOK as catalyst.From the variation of the equilibrium constant with temperature, the values of the thermodynamic parameters ΔG, ΔH and ΔS of isomerization at 298.15 K were evaluated.The propenyl ethers are highly favored at equilibrium, the values of both ΔG and ΔH for the allyl -> propenyl reaction being ca. -18 to 25 kJ mol-1.The favor of the propenyl ethers is increased by bulky alkyl substituents, and decreased by methoxysubstituted alkyl groups.In most cases the entropy contribution is negligible; however, for R=(MeO)2CH and R=(MeO)3C the values of ΔS are ca. -5 J K-1 mol1-.
- Taskinen, Esko
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p. 11389 - 11394
(2007/10/02)
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