Dialkyltitanium-mediated titanation of conjugated 1,3-butadiynes and its coupling reactions with aldehydes: a facile synthesis of stereodefined enynes and trans-enynols

Insertion of nitriles into zirconocene 1-aza-1,3-diene complexes: chemoselective synthesis of N-H and N-substituted pyrroles

The direct insertion of nitriles into zirconocene-1-aza-1,3-diene complexes provides an efficient, chemoselective, and controllable synthesis of N-H and N-substituted pyrroles upon acidic aqueous work-up. The outcome of the reaction (that is, the formation of N-H or N-substituted pyrroles) results from the different cyclization patterns, which depend on the relative stability and reactivity of the enamine-imine tautomers formed by hydrolysis of the diazazirconacycles.

Titanium-mediated cross-coupling reactions of 1,3-butadiynes with α-iminonitriles to 3-aminopyrroles: observation of an imino aza-Nazarov cyclization

Ti(OⁱPr)₄/2 ⁿBuLi-mediated highly efficient cross-coupling reactions of 1,3-butadiynes with α-iminonitriles are described, which provide convenient access to functionalized 3-aminopyrroles.

(E)-1,5-Di-phenyl-pent-2-en-4-yn-1-one

The title compound, C₁₇H₁₂O, has an E conformation about the C=C bond. The C—C C—C torsion angle is 7.7 (2)°, and the mean planes of the phenyl­ethyl­enone [r.m.s. deviation = 0.059 (1) Å] and phenyl­acetyl­ene [r.m.s. deviation = 0.023 (1) Å] fragments form a dihedral angle of 14.16 (7)°. In the crystal, weak C—H⋯O inter­actions link the mol­ecules into zigzag chains propagated in [010].

Titanium-mediated reductive cross-coupling reactions of imines with terminal alkynes: An efficient route for the synthesis of stereodefined allylic amines

Low-valency titanium species, generated in situ by using Ti(OiPr)₄/2 c-C₅H₉MgCl reagent, react with imines to give a titanium-imine complex that can couple with terminal alkynes to provide azatitanacyclopentenes with excellent regioselectivity. Stereodefined allylic amines are obtained in good yields after hydrolysis or iodonolysis of the corresponding azatitanacyclopentenes. When ethynylcyclopropane is used as the coupling partner to react with imines in this reaction, the initially generated allylic amine undergoes an unexpected 1,3-amino migration on silica gel during the column chromatography.

Unexpected zirconium-mediated multicomponent reactions of conjugated 1,3-butadiynes and monoynes with acyl cyanide derivatives

Going ber(zirc): zirconium-butadiyne complexes react with acyl cyanide derivatives through diverse reaction pathways. The complexes react with two molecules of carbamoyl cyanide to form 1,4-benzodiazepin-2-one-derivatives containing azazirconacycles. Reactions with either aroyl cyanides or alkyl cyanoformates lead to azazirconacyclopentenes containing a quaternary carbon center.

Stereoselective synthesis of enynones via base-catalyzed isomerization of 1,5-disubstituted-2,4-pentadiynyl silyl ethers or their alcohol derivatives

1,5-Disubstituted-2,4-pentadiynyl silyl ethers undergo smooth desilylative isomerization to afford cis-enynones as major products with moderate stereoselectivities in the presence of a catalytic amount of KO(t)Bu or DBU. While the isomerization reactions of their alcohol derivatives catalyzed by KOH, KO(t)Bu or NaH take place efficiently to produce trans-enynones with high stereoselectivities. These reactions provide convenient and practical routes for the synthesis of enynones with a wide range of substitution groups.