| Summary: | The reduction of <i>N</i>,<i>N</i>-disubstituted 2-alkynylamines and substituted 3-alkynylols using the NbCl<sub>5</sub>–Mg reagent system affords the corresponding dideuterated (2<i>Z</i>)-alkenylamine and (3<i>Z</i>)-alkenylol derivatives in high yields in a regio- and stereoselective manner through the deuterolysis (or hydrolysis). The reaction of substituted propargylamines and homopropargylic alcohols with the in situ generated low-valent niobium complex (based on the reaction of NbCl<sub>5</sub> with magnesium metal) is an efficient tool for the synthesis of allylamines and homoallylic alcohols bearing a 1,2-disubstituted double bond. It was found that the well-known approach for the reduction of alkynes based on the use of the TaCl<sub>5</sub>-Mg reagent system does not work for 2-alkynylamines and 3-alkynylols. Thus, this article reveals a difference in the behavior of two reagent systems—NbCl<sub>5</sub>-Mg and TaCl<sub>5</sub>-Mg, in relation to oxygen- and nitrogen-containing alkynes. A regio- and stereoselective method was developed for the synthesis of nitrogen-containing <i>E</i>-β-chlorovinyl sulfides based on the reaction of 2-alkynylamines with three equivalents of methanesulfonyl chloride in the presence of stoichiometric amounts of niobium(V) chloride and magnesium metal in toluene.
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