The reaction of lithiated (R)-2-(trimethylsilyl)ethyl p-tolyl sulfoxide 1 with α,β-unsaturated esters gives 1,4-conjugate addition products as single stereoisomers, whereas the reaction of 1 with 4-, 6-, or 7-haloalkenoates affords cyclopropane-, cyclopentane- or cyclohexanecarboxylates, respectively, with high stereoselectivity.