Diisopropoxytitanium dichloride

Unsaturated acyl oxazolidinones 1 undergo enantiospecific [2 + 2] cycloadditions with 1,1-di-methylthioethylene and a catalyst consisting of a 1 1 mixture of diisopropoxytitanium dichloride and the chiral diol 243,44. The cyclobutane 3 is obtained in excellent yield with high enantiomeric excess. This is the first example of the enantiospecific [2 + 2] cycloaddition yielding a cyclobutane using an external chiral auxiliary as a chiral catalyst. Unfortunately, the scope of this reaction is quite limited since it fails with vinyl ethers, silyl enol ethers and ketene silyl acetals. 

Diisopropoxytitanium(IV) dibromide Is prepared following the preparative procedure for diisopropoxytitanium(IV) dichloride.2... 

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