Regioselective opening of epoxy alcohols: mild chemo- and stereoselective preparation of iodohydrins and 1,2-diols
摘要:
Several 2,3-epoxy alcohols have been opened, at -60-degrees-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 iodide ion.
Erbium(III) Triflate is a Highly Efficient Catalyst for the Synthesis of β-Alkoxy Alcohols, 1,2-Diols and β-Hydroxy Sulfides by Ring Opening of Epoxides
ring-opening reaction of epoxides with erbium(III) triflate are described. Epoxides can be cleaved under neutral conditions with alcohols and thiols in the presence of catalytic amounts of Lewis acid, affording the corresponding β-alkoxy alcohols and β-hydroxy sulfides in high yields. In water, epoxide ring opening occurs to produce the corresponding diols in good yields epoxides - Lewis acids - nucleophilic
An efficient one‐pot method for the selective benzylation of diols and polyols using 0.1 equiv. of organotin reagents and tetrabutylammonium bromide as catalyst has been developed. The diols and polyols containing a cis‐vicinal diol were regioselectively benzylated in 70–94% isolated yields. A catalytic reaction mechanism was also proposed.