Highly Regio- and Diastereoselective Formation of Tetrasubstituted (Z)-1,2-Dihaloalkenes from the Halogenation of Trimethylsilyl Alkynes with ICl

The stereoselective anti addition of diatomic halogens to alkynes has been well studied. A method is reported that utilizes the β-silyl effect to override this typically observed anti selectivity and provides halogenation products that result from syn addition. The reaction involves the addition of iodine monochloride to trialkylsilyl-substituted alkynes to produce tetrasubstituted (Z)-dihaloalkenes in good to excellent yields and with excellent regio- and diastereoselectivity.