Alpha-selective Ni-catalyzed hydroalumination of aryl- and alkyl-substituted terminal alkynes: practical syntheses of internal vinyl aluminums, halides, or boronates.
A method for Ni-catalyzed hydroalumination of terminal alkynes, leading to the formation of alpha-vinylaluminum isomers efficiently (>98% conv in 2-12 h) and with high selectivity (95% to >98% alpha), is described. Catalytic alpha-selective hydroalumination reactions proceed in the presence of a reagent (diisobutylaluminum hydride; dibal-H) and 3.0 mol % metal complex (Ni(dppp)Cl(2)) that are commercially available and inexpensive. Under the same conditions, but with Ni(PPh(3))(2)Cl(2), hydroalumination becomes highly beta-selective, and, unlike uncatalyzed transformations with dibal-H, generates little or no alkynylaluminum byproducts. All hydrometalation reactions are reliable, operationally simple, and practical and afford an assortment of vinylaluminums that are otherwise not easily accessible. The derived alpha-vinyl halides and boronates can be synthesized through direct treatment with the appropriate electrophiles [e.g., Br(2) and methoxy(pinacolato)boron, respectively]. Ni-catalyzed hydroaluminations can be performed with as little as 0.1 mol % catalyst and on gram scale with equally high efficiency and selectivity.
Gao
Fang
F
Department of Chemistry, Merkert Chemistry Center, Boston College, Chestnut Hill, Massachusetts 02467, USA.
Hoveyda
Amir H
AH
D000480:Alkynes / Q000737:chemistry*; D000535:Aluminum / Q000737:chemistry*; D001897:Boronic Acids / Q000737:chemistry*; D002384:Catalysis; D006219:Halogens / Q000737:chemistry*; D009532:Nickel / Q000737:chemistry*; D013237:Stereoisomerism; D013379:Substrate Specificity; D014753:Vinyl Compounds / Q000737:chemistry*
D000480:Alkynes; D001897:Boronic Acids; D006219:Halogens; D014753:Vinyl Compounds; D009532:Nickel; D000535:Aluminum