HIGHLY SELECTIVE RING-OPENING OF 1,3,3-TRIHALOGENOEPOXYCYCLOHEXANES BY BORON TRIHALIDES - METHODOLOGY FOR THE DETERMINATION OF THE REGIOSELECTIVITY IN THE CYCLIZATION OF 2,2,6,6-TETRAHALOGENOCYCLOHEXANOLS

Reaction of 1,3,3-trihalogeno-7-oxabicyclo[4.1.0]heptanes with boron t rihalides (F, Cl, Br) resulted in the regio- and stereo-selective form ation in high yield of the corresponding tetrahalohydrins. In these re actions the hypervalent halogenoborate species are responsible for the selective halogenation of the epoxides by cis opening. A methodology is given to predict the regioselectivity in the epoxidic cyclisation o f 2,2,6,6-tetrahalogenocyclohexanols. These processes allowed the prep aration of all the isomers of 1,3,3-trihalogeno-7-oxabicyclo[4.1.O]hep tanes or 2,2,6,6-tetrahalogenocyclohexanols (X = Cl, F), very useful i ntermediates.