- Ring-opening cyclization of spirocyclopropanes using sulfoxonium ylides
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Ring-opening cyclization of cyclohexane-1,3-dione-2-spirocyclopropanes using dimethylsulfoxonium methylide proceeded regioselectively to produce 2,3,4,6,7,8-hexahydro-5H-1-benzopyran-5-ones in good to high yields. The reactions of cycloheptane- and cyclopentane-1,3-dione-2-spirocyclopropanes could construct [7.6]- and [5.6]-fused ring systems. This reaction was also carried out using sulfoxonium ethylide, butylide, and benzylide, resulting in the formation of the corresponding 2,3-trans-disubstituted products in good to high yields, and it was shown that the dimethyl group can act as a dummy substituent. It was found that the 2- and 3-phenyhexahydrobenzopyran-5-ones can be readily converted into 5-hydroxyflavan and 5-hydroxy-isoflavan, respectively.
- Onuki, Yuta,Nambu, Hisanori,Yakura, Takayuki
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p. 479 - 486
(2020/09/09)
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- 1,2-Diarylethanols by alternative regioselective reductive ring-opening of 2,3-diaryloxiranes
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Non-symmetrical £rans-2,3-diaryloxiranes have been regioselectively opened by catalytic hydrogenation over Pd/C, NaBH4/Pd and [Cp 2TiCl]/H2O. Although in the catalytic hydrogenation reactions the epoxides were mainly opened at the β-carbon with respect to the substituted aryl ring in all cases, with the [Cp2TiCl]/H 2O system the regioselectivity was affected by the electronic properties of the aryl residues, the epoxides being opened on the carbon bearing the most electron-releasing or the least electron-withdrawing group. With the NaBH4/Pd system different regioisomers were obtained depending on the substituents. Starting from enantioenriched epoxides, no loss of optical purity was observed in the alcohols formed.
- Blasio, Nadia Di,Lopardo, Maria Teresa,Lupattelli, Paolo
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scheme or table
p. 938 - 944
(2009/07/19)
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- Synthesis and reactivity of benzylic sulfonium salts: Benzylation of phenol and thiophenol under near-neutral conditions
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A series of benzyldimethylsulfonium - and related hydrogensulfate salts have been synthesized from the ternary system ArCH2OH:H2SO4: Me2S or tetrahydrothiophene. The salts are generally stable crystalline solids, but anomalously high reactivity is observed for 9-(anthrylmethyl)dimethylsulfonium hydrogensulfate. Selected sulfonium salts have been used for the O- and S-benzylation of phenol and thiophenol, respectively, in a two phase system under near-neutral conditions. The benzylation of oximes and benzimidazole under basic conditions is also described.
- Forrester,Jones,Newton,Preston
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p. 2871 - 2884
(2007/10/03)
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- Metalation of o-Halostyrene Oxides. Preparation of Benzocyclobutenols
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o-Bromo- and o-iodostyrene oxides are converted in fair to good yield to benzocyclobutenols upon treatment with n-BuLi and MgBr2 in THF or ether at -78 deg C, followed by warming to room temperature.The reaction involves initial halogen-lithium exchange followed either by MgBr2-initiated opening of the epoxide function to a haloalkoxide or rearrangement of the epoxide function to a ketone or aldehyde followed by cyclization.Benzocyclobutenol formation was not successful in the case of o-halostilbene oxides.
- Akguen, Eyup,Glinski, Margaret B.,Dhawan, Kasturi L.,Durst, Tony
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p. 2730 - 2734
(2007/10/02)
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- Process for the purification of epoxy compounds
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The low molecular water-soluble onium-catalyst dissolved in the liquid mixture of epoxy resin and excess epihalohydrin obtained by the reaction in the presence of base of a compound having --OH, --SH, --COOH or =NH groups with excess 1-halo-2,3-epoxyalkane, is separated therefrom by contacting the liquid mixture, either prior to or after separation therefrom of the precipitated salt produced by the reaction, with at least about 5 parts by weight based on the weight of the catalyst present in the liquid mixture, of an adsorbent containing or capable of absorbing at least 1% by weight of water so strongly that it cannot be removed either by drying over concentrated sulfuric acid or by drying at 110° C. and can only be partially removed by drying at 200° C. under vacuum (about 1 millibar), and then separating the adsorbent with catalyst adsorbed thereon from the liquid mixture.
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