Rare-Earth Silylamide-Catalyzed Selective Dimerization of Terminal Alkynes and Subsequent Hydrophosphination in One Pot

Rare-earth silylamides, Ln[N(SiMe3)2]3 (Ln = Y, La, Sm), catalyzed regio- and stereoselective dimerization of terminal alkynes in the presence of amine additives to give conjugated enynes in high yields. The additives played a crucial role to depress the oligomerization and to control the regio- and stereochemistry of the dimerization. Thus, the selectivity for (Z)-head-to-head enynes was increased in the order of tertiary < secondary < primary amine additives. On the other hand, the reversed order was observed for the formation of head-to-tail dimers. When α,ω-diynes were subjected to the dimerization, very novel cyclic bisenyne compounds were given through double-dimerization in satisfactory yields. In addition, an application of the system allowed subsequent hydrophosphination of the enynes generated in situ with diphenylphosphine, giving rise to 1-phosphinyl-1,3-dienes as the sole products in excellent yields after oxidative workup

Rare-Earth Silylamide-Catalyzed Selective Dimerization of Terminal Alkynes and Subsequent Hydrophosphination in One Pot

Rare-earth silylamides, Ln[N(SiMe3)2]3 (Ln = Y, La, Sm), catalyzed regio- and stereoselective dimerization of terminal alkynes in the presence of amine additives to give conjugated enynes in high yields. The additives played a crucial role to depress the oligomerization and to control the regio- and stereochemistry of the dimerization. Thus, the selectivity for (Z)-head-to-head enynes was increased in the order of tertiary < secondary < primary amine additives. On the other hand, the reversed order was observed for the formation of head-to-tail dimers. When α,ω-diynes were subjected to the dimerization, very novel cyclic bisenyne compounds were given through double-dimerization in satisfactory yields. In addition, an application of the system allowed subsequent hydrophosphination of the enynes generated in situ with diphenylphosphine, giving rise to 1-phosphinyl-1,3-dienes as the sole products in excellent yields after oxidative workup

Dehydrogenative Silylation of Amines and Hydrosilylation of Imines Catalyzed by Ytterbium−Imine Complexes

Dehydrogenative silylation of primary and secondary amines with triphenylsilane was catalyzed by ytterbium−imine complexes, [Yb(η2-Ph2CNAr)(hmpa)n], to give aminosilanes in good yields. In the reaction with diphenyl- and phenylsilanes, diaminosilanes were formed as major products. Whereas n- and sec-alkylamines were readily silylated, tert-alkylamines and aromatic amines exhibited lower reactivities. Moreover, hydrosilylation of imines has been achieved by using phenylsilane and the imine complexes (Ar = Ph, C6H4F-4), giving rise to mono- and diaminosilanes. The two reactions were in agreement as regards the product selectivities and yields

Dehydrogenative Silylation of Terminal Alkynes Catalyzed by Ytterbium−Imine Complexes

Catalytic dehydrogenative silylation of terminal alkynes with hydrosilanes has been achieved by using divalent Yb−imine complexes. The reaction with mono-, di-, and trihydrosilanes gave the corresponding alkynylsilanes in good yields. α,ω-Diynes were similarly silylated at both termini. Thus, oligomers were obtained from the diynes and dihydrosilanes. In addition, it has been found that the imine complexes exhibit catalytic activity for redistribution of the silyl groups of the alkynylsilanes and for Si−Si bond fission of disilanes

Regio- and Stereochemistry on the Electrophilic Trapping of Allylic Samariums Generated by Reductive Cleavage of Allylic Ethers with (C₅Me₅)₂Sm(thf)_<i>n</i>

The C−O bond of allylic benzyl ethers was selectively cleaved with Cp*2Sm(thf)n to give allylic samarium complexes in good yields. Facility of their bond fission has been found to be comparable to that of the corresponding propargylic ethers intermolecularly, but lower intramolecularly. Regio- and stereochemistry on the electrophilic trapping of the allylic complexes thus generated remarkably depended on the nature of the electrophiles. They reacted with carbonyl compounds exclusively from the most substituted terminus of the allylic moieties to yield blanched homoallylic alcohols with anti diasteroselectivity. On the other hand, trapping with silyl chlorides produced linear allylic silanes. Here, a plausible mechanism to account for the difference is proposed

Three-Component Coupling of Acylphosphonates and Two Carbonyl Compounds Promoted by Low-Valent Samariums: One-Pot Synthesis of β-Hydroxyphosphonates

Three-component coupling of acylphosphonates and two carbonyl compounds leading to β-hydroxyphosphonates has been achieved with low-valent samariums. Thus, acylphosphonates reacted with aldehydes in the presence of semicatalytic amounts of samarium metal or SmI2 to give acyloxyphosphonates in good yields. The second coupling reaction of the acyloxyphosphonates with aldehydes or ketones promoted by SmI2 afforded β-hydroxyphosphonates instead of olefins. Moreover, these two reactions could be carried out in one pot