Treatment of 1-chlorovinyl p-tolyl sulfoxides, which were synthesized from ketones and chloromethyl p-tolyl sulfoxide, with ethylmagnesium chloride or isopropylmagnesium chloride at below −78 °C gave magnesium alkylidene carbenoids in about 90% yields. The reaction of the generated carbenoids with lithium α-sulfonyl carbanions was found to afford tri- and tetra-substituted allenes. Both cyclic ketones and acyclic ketones were useful in this procedure. However, the 1-chlorovinyl p-tolyl sulfoxides derived from aldehydes gave only rearranged products, acetylenes, under the reaction conditions. The magnesium alkylidene carbenoid derived from an optically active 1-chlorovinyl p-tolyl sulfoxide was treated with lithium α-carbanion of 1-naphthyl phenyl sulfone; however, the obtained allene was found to be racemic. The mechanism of this reaction is also discussed.