Highly regioselectiveringopenings of 2,3-epoxyalcohols have been performed by use of zeolite-supported ammoniumhalides or sodiumbenzenethiolate; the reactivities of these reagents are highly dependent on the conditions of their preparation.
In an attempt to replace harmful or carcinogenic solvents (such as dichloromethane, acetone, etc.) with non-harmful and greener ones, the possibility of performing four already developed ring-opening methodologies in a more eco-friendly media, such as DMC, has been investigated. The results show that the usual employed solvents (CH2Cl2, Et2O, CH3CN, etc.) can be easily replaced by DMC: not only the stereo- and regioselectivity is conserved, but also the work-up is simplified to a filtration, therefore reducing considerably the amount of solvents employed in the processes, and all the reactions are performed at room temperature, even the ones previously reported at low temperatures.
Solvent Dependency in Regioselective Ring Openings of 3,4- and 2,3-Epoxy Alcohols with Diethylamine Hydrohalides
作者:Lian-xun Gao、Akio Murai
DOI:10.1246/cl.1991.1503
日期:1991.9
Titanium-mediated ringopenings of 3,4-epoxy-1-ols at the 4-position with diethylamine hydrohalides proceeded efficiently in dichloromethane, while the requisite openings of 2,3-epoxy-1-ols at the 3-position in benzene.
The first C2 selective halide substitution reactions of 2,3-epoxy alcohols have been realized by the use of the (CH3O)3B–MX (X=I, Br, Cl) system, which proceed through novel endo-mode epoxide-opening of intramolecular boron chelates to afford the corresponding C2 halohydrin derivatives with high regio- and stereoselectivity.