- Investigation of diastereoselective acyclic α-alkoxydithioacetal substitutions involving thiacarbenium intermediates
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Reported herein is an experimental and theoretical study that elucidates why silylated nucleobase additions to acyclic α-alkoxythiacarbenium intermediates proceed with high 1,2-syn stereocontrol (anti-Felkin-Anh), which is opposite to what would be expected with corresponding activated aldehydes. The acyclic thioaminals formed undergo intramolecular cyclizations to provide nucleoside analogues with anticancer and antiviral properties. The factors influencing the selectivity of the substitution reaction have been examined thoroughly. Halothioether species initially form, ionize in the presence (low dielectric media) or absence (higher dielectric media) of the nucleophile, and react through SN2-like transition structures (TS A and D), where the α-alkoxy group is gauche to the thioether moiety. An important, and perhaps counterintuitive, observation in this work was that calculations done in the gas phase or low dielectric media (toluene) are essential to locate the product- and rate-determining transition structures (C-N bond formation) that allow the most reasonable prediction of selectivity and isotope effects for more polar solvents (THF, MeCN). The ΔΔG? (GTSA-TSD) obtained in silico are consistent with the preferential formation of 1,2-syn product and with the trends of stereocontrol displayed by 2,3-anti and 2,3-syn α,β-bis-alkoxydithioacetals.
- Prvost, Michel,Dostie, Starr,Waltz, Marie-ve,Guindon, Yvan
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p. 10504 - 10525
(2015/02/19)
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- Synthesis of dithioacetals and oxathioacetals with chiral auxiliaries
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One-pot synthesis of dithioacetals as well as an efficient method for oxathioacetal is reported. Additionally, some chiral auxiliaries were used to synthesize enantiomerically pure dithioacetals and oxathioacetals.
- Zaidi, Javid H.,Naeem, Fazal,Khan, Khalid M.,Iqbal, Rasfaid,Zia-Ullah
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p. 2641 - 2653
(2007/10/03)
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- Reactions of Sulfoxides with Magnesium Amides. Transformations of Sulfoxides into Sulfides, Dithioacetals and Vinyl Sulfides
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The reactions of sulfoxides with magnesium amides generated in situ from the reaction of ethylmagnesium bromide and seconday amines, such as diisopropylamine (DIPA) or 2,2,6,6-tetramethylpiperidine (TMP) in diethyl ether, were examined.Diaryl sulfoxides were heated with the diisopropylaminomagnesium reagent in diethyl ether to give the corresponding diaryl sulfides in 42-52percent yields.Sulfoxides bearing hydrogens at the α-position only(RSOCH2R1) reacted with the tetramethylpiperidinomagnesium reagent at room temperature to produce the corresponding dithioacetals (RSCHR1SR) in 47-86percent yields.The treatment of sulfoxides bearing hydrogens both at the α-and β-positions (RSOCHR1CHR2R3) with the magnesium amides at room temperature afforded the corresponding vinyl sulfides (RSCR1=CR2R3) in 52-72percent yields accompanying 2.3-27percent yields of the corresponding dithioacetals.The pathways leading to the products involving the formation of the sulfur-stabilized carbonium ion intermediates are discussed.
- Kobayashi, Kazuhiro,Kawakita, Masataka,Yokota, Kouichi,Mannami, Tohru,Yamamoto, Koji,et al.
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p. 1401 - 1408
(2007/10/02)
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- Formation of Dithioacetals by Treatment of Sulfoxides Carrying α-Hydrogens with Magnesium Amides
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Sulfoxides carrying α-hydrogens were allowed to react with magnesium amides generated in situ by the treatment of ethylmagnesium bromide with secondary amines such as 2,2,6,6-tetramethylpiperidine or diisopropylamine in diethyl ether to give the corresponding dithioacetals in moderate to good yields.
- Kobayashi, Kazuhiro,Kawakita, Masataka,Mannami, Tohru,Morikawa, Osamu,Konishi, Hisatoshi
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p. 1551 - 1554
(2007/10/02)
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- Static and dynamic structures of pentacarbonyl-chromium(0) and -tungsten(0) complexes of dithioether ligands I. Symmetrical dithioether complexes and X-ray crystal structure of
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The complexes (M=Cr, R=Et, iPr, t-Bu; M=W, R=Me, Et, iPr, t-Bu) were synthesised.Total bandshape NMR analysis was used to measure energies of inversion of the coordinated S atom in the tungsten complexes. ΔG (298.15 K) values were in the range 34-42 kJ mol-1.An X-ray structure of was obtained.
- Abel, Edward W.,Orrell, Keith G.,Rahoo, Haji,Sik, Vladimir,Mazid, Mohammed A.,Hursthouse, Michael B.
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p. 191 - 199
(2007/10/02)
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