- Oxygen-directed intramolecular hydroboration
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Metal-free homoallylic oxygen-directed intramolecular hydroboration is reported. Regioselectivities from 20:1 to 82:1 favoring the 1,3-dioxy-substituted products have been achieved using Me2S·BH3/TfOH followed by standard oxidative workup. Branching at the C5 position improves regioselectivity. Copyright
- Rarig, Robert-Andre F.,Scheideman, Matthew,Vedejs, Edwin
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supporting information; body text
p. 9182 - 9183
(2009/02/03)
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- Regioselective nucleophilic ring opening of epoxides and aziridines derived from homoallylic alcohols
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The regioselectivity of nuclcopbilic ring opening of some 3,4-epoxy and 3,4-aziridino alcohols has been studied. The nucleophiles chosen were complex hydrides (LiAlH4, Red-Al and DIBAL) and Lipshutz- or Gilman-type organocuprate reagents. The C-4 substituent in the substrates was varied in order to study steric and electronic effects on the ring opening reactions. For alkyl substituents at C-4, most of the results can be explained on the basis of intramolecular delivery of the nucleophile to C-3 via a six-membered transition state, leading to 1,4-diols or 1,4-amine alcohol derivatives. In general, the epoxy alcohols gave poorer regioselectivity than the N-tosyl aziridino alcohols, for which selectivities of >95:5 were routinely obtained. The activating effect of a phenyl group at C-4 led to a switch in regiochemistry, with the 1,3-diol or 1,3-amino alcohol derivative as the major product.
- Tanner, David,Groth, Thomas
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p. 16139 - 16146
(2007/10/03)
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- Regioselective Opening of Epoxy Alcohols: Mild Chemo- and Stereoselective Preparation of Iodohydrins and 1,2-Diols
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Several 2,3-epoxy alcohols have been opened, at -60 deg C, with MgI2, leading to the corresponding 3-iodo 1,2-diols with a high level of regio- and chemoselectivity.The iodohydrins can be reduced "in situ", by means of nBu3SnH, to the corresponding 1,2-diols.The chemo-, regio-, and stereocontrol of the reaction makes the method of wide use.Furthermore, epoxy alcohol derivatives (acetyl, benzyl, or TBMS) still maintain a strong preference for C-3 attack of the nucleophile.The experimental data strongly suggest that a metal (Mg) centered chelate is formed throughout the reaction, which gives rise to the regioselective delivery of the iodiode ion.
- Bonini, Carlo,Righi, Giuliana,Sotgiu, Giovanni
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p. 6206 - 6209
(2007/10/02)
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- Regioselective reductive opening of 2,3-epoxy alcohol derivatives with lithium borohydride in a solid state
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2,3-Epoxy alcohol derivatives were reduced regiospecifically with lithium borohydride in a solid state suspended in hexane to yield the corresponding C-3 opening products.
- Sugita, Keisuke,Onaka, Makoto,Izumi, Yusuke
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p. 7467 - 7468
(2007/10/02)
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