Diastereoselective halolactonization

Synthesis of Morpholin-2,5-diones via Diastereoselective Halolactonization Mediated by L-Proline Derivatives... 

If the alkylation products 3 contain appropriately placed double bonds, they can subsequently be subjected to halolactonization with high diastereoselectivity to furnish mixtures of chiral diastereomeric lactones, e.g., 4, along with the chiral auxiliary. 

The conversion of an alkene to a halohydrin can also be considered as an epoxidation because this can be achieved by a simple ring closure.184 Although no reagent is yet available to perform an asymmetric conversion of an isolated alkene to a halohydrin, the reaction can be controlled through diastereoselection. One such case is the halolactonization of y,8-unsaturated carboxylic acids, N,N-dialkylamides.185189... 

Haloetherification is closely related to halolactonization although it is used less often. Its main application is the diastereoselective synthesis of synthetically useful substituted tetrahy-drofurans. The mechanism of the asymmetry transfer of the reaction has been investigated using a transition-structure model based on AM1 calculations167. The strong correlation between model and experimental results makes the proposed rationale extremely attractive. 

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