NbCl5-Mg Reagent System in Regio- and Stereoselective Synthesis of (2Z)-Alkenylamines and (3Z)-Alkenylols from Substituted 2-Alkynylamines and 3-Alkynylols.

The reduction of N,N-disubstituted 2-alkynylamines and substituted 3-alkynylols using the NbCl5-Mg reagent system affords the corresponding dideuterated (2Z)-alkenylamine and (3Z)-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 NbCl5 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 TaCl5-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-NbCl5-Mg and TaCl5-Mg, in relation to oxygen- and nitrogen-containing alkynes. A regio- and stereoselective method was developed for the synthesis of nitrogen-containing E-ß-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.

Cp2ZrCl2 - Et3Al reagent system in the homo-coupling of trimethylsilyl-substituted alkynes.

The reaction of trimethylsilyl-substituted alkynes with 0.5 equivalents of Cp2ZrCl2 and 1 equivalent of Et3Al in toluene at room temperature for 18 hours gives, after hydrolysis/deuterolysis or iodination, functionalized products of the homo-coupling of silyl-substituted alkynes in good yield. Trimethylsilyl-substituted α,ω-diynes react with the Cp2ZrCl2 - Et3Al reagent system to give (1Z,2Z)-1,2-bis(iodo(trimethylsilyl)methylene)cycloalkanes after iodinolysis.

Niobium- and zirconium-catalyzed reactions of substituted 2 alkynylamines with Et2Zn.

The NbCl5-EtMgBr-catalyzed reaction of N,N-disubstituted 2-alkynylamines with Et2Zn followed by hydrolysis or deuterolysis affords (2Z)-alkenylamines (reduction products of alkyne) in high yields. The reaction of N,N-disubstituted 2-alkynylamines with Et2Zn catalyzed by the Cp2ZrCl2-EtMgBr system occurs as 2-zincoethylzincation, resulting, after deuterolysis or iodinolysis, in the regio- and stereoselective formation of the corresponding dideuterated and diiodinated 2-alkenylamine derivatives with a trisubstituted double bond. This study demonstrates the difference between the catalytic effects of NbCl5 and Cp2ZrCl2 on the pathway of reaction of tertiary 2-alkynylamines with Et2Zn in the presence of catalytic amounts of EtMgBr.

Synthesis of heteroatom-containing pyrrolidine derivatives based on Ti(O-iPr)4 and EtMgBr-catalyzed carbocyclization of allylpropargyl amines with Et2Zn.

The Ti(O-iPr)4 and EtMgBr-catalyzed regio and stereoselective carbocyclization of N-allyl-substituted 2-alkynylamines with Et2Zn, followed by deuterolysis or hydrolysis, affords the corresponding methylenepyrrolidine derivatives in high yields. It was found that Ti-Mg-catalyzed carbocyclization of N-allyl-substituted 2-alkynylamines with Et2Zn is equally selective in dichloromethane, hexane, toluene, and diethyl ether. The reaction was tolerant to the presence of aryl, alkyl, trimethylsilyl, methoxymethyl and aminomethyl substituents on the alkyne. A selective method was proposed for the preparation of bis-pyrrolidine derivatives using Ti-Mg-catalyzed carbocyclization of bis-allylpropargyl amines with Et2Zn.