22422-17-9Relevant articles and documents
Titanium silicates as efficient catalyst for alkylation and acylation of silyl enol ethers under liquid-phase conditions
Sasidharan, Manickam,Bhaumik, Asim
experimental part, p. 87 - 93 (2011/10/12)
The activity of titanium- and tin-silicate samples such as TS-1, TS-2, Ti-β and Sn-MFI has been investigated for acylation and alkylation of silyl enol ethers under mild liquid-phase conditions. Silyl enol ethers successfully react with acetyl chloride and tert-butyl chloride under dry conditions in the presence of above catalysts to produce the corresponding acylated and alkylated products, respectively. In the case of acetylation reaction, two different nucleophiles with carbon-center (C-atom) and oxygen-center (O-atom) in silyloxy group of silyl enol ether reacts with acetyl chloride to give 1,3-diketone and ketene-ester, respectively. The selectivity for alkylation is always ca. 100% and no side products are formed. Among the various solvents investigated, anhydrous THF was found to be the suitable solvent for alkylation; whereas dichloromethane exhibited high selectivity for diketones for acylation. The formation of nucleophiles from silyl enol ethers appears to be the key step for successful acetylation and tert-butylation by nucleophilic reaction mechanism. Sn-MFI showed less activity than that observed over the titanosilicates. The observed catalytic activity is explained on the basis of "oxophilic Lewis acidity" of titanium silicate molecular sieves in the absence of H 2O under dry reaction conditions.
Elimination-addition mechanism for nucleophilic substitution reaction of cyclohexenyl iodonium salts and regioselectivity of nucleophilic addition to the cyclohexyne intermediate
Fujita, Morifumi,Kim, Wan Hyeok,Sakanishi, Yuichi,Fujiwara, Koji,Hirayama, Sayaka,Okuyama, Tadashi,Ohki, Yasuhiro,Tatsumi, Kazuyuki,Yoshioka, Yasunori
, p. 7548 - 7558 (2007/10/03)
The reaction of 4-substituted cyclohex-1-enyl(phenyl)iodonium tetrafluoroborate with tetrabutyl-ammonium acetate gives both the ipso and cine acetate-substitution products in aprotic solvents. The isomeric 5-substituted iodonium salt also gives the same mixture of the isomeric acetate products. The reaction is best explained by an elimination-addition mechanism with 4-substituted cyclohexyne as a common intermediate. The cyclohexyne formation was confirmed by deuterium labeling and trapping to lead to [4 + 2] cycloadducts and a platinum-cyclohexyne complex. Cyclohexyne can also be generated in the presence of some other mild bases such as fluoride ion, alkoxides, and amines, though amines are less effective bases for the elimination. Kinetic deuterium isotope effects show that the anionic bases induce the E2 elimination (k H/kD > 2), while the amines allow formation of a cyclohexenyl cation in chloroform to lead to E1 as well as SN1 reactions (k H/kD ≈ 1). Bases are much less effective in methanol, and methoxide was the only base to efficiently afford the cyclohexyne intermediate. Nucleophiles react with the cyclohexyne to give regioisomeric products in the ratio dependent on the ring substituent. The observed regioselectivity of nucleophilic addition to substituted cyclohexynes is rationalized from calculated LUMO populations, which are governed by the bond angles at the acetylenic carbons: The less deformed carbon has a higher LUMO population and is preferentially attacked by the nucleophile.
Cyclohexynes. Generation from iodonium salts and regioselective reaction with nucleophile
Fujita, Morifumi,Sakanishi, Yuichi,Kim, Wan Hyeok,Okuyama, Tadashi
, p. 908 - 909 (2007/10/03)
Cyclohexynes are effectively generated by treatment of cyclohex-1-enyliodonium salts with a mild base such as acetate and fluoride ion in chloroform. Regioselectivity of the nucleophilic addition of acetate ion to cyclohexynes depends on the 4-substituent
