Preparation of Dienylstannanes Via Pd Catalyzed Regio- and Stereocontrolled Addition Reactions
作者:Barry M. Trost、Chao-Jun Li
DOI:10.1055/s-1994-25678
日期:——
Using palladium-catalyzed addition reactions, a terminal alkyne, an alkynoate, and a tin hydride comprise the building blocks for the construction of 4-stannyl-(E,E)-2,4-dienoates in an atom-economical fashion. A terminal alkyne undergoes clean cis-1,2-addition to an internal alkynoate in the presence of catalytic palladium(II) acetate and tris(2,6-dimethoxyphenyl)phosphine to produce a 2-en-4-ynoate. Anti-Markovnikov cis-addition of tin hydride to the acetylenic function of the 2-en-4-ynoate occurs in the presence of in situ generated tetrakis(triphenylphosphine)palladium.
[reaction: see text] A new and efficient procedure for the preparation of unsymmetrical silaketals via a three-step protocol without isolation of the intermediates is presented. The unsymmetrical silyl ethers and silanes can also be readily obtained via this sequence of reactions.
In sharp contrast with the standard [2 + 2 + 2] cycloadditionreaction of diyne/ene, cobalt-mediated cycloadditions with γ-alkylidenebutenolide led to unprecedented cobalt(III) polycyclic complexes. A plausible mechanism supported by a computational study based on an unusual fragmentation of the butenolide moiety was postulated to account for this original reaction.
The ubiquitary Co(I) complex CoCl(PPh3)3 was found to be a convenient catalyst for the [2 + 2 + 2] cycloaddition of functionalized triynes under mild reaction conditions and devoid of any additional additive, yielding the substituted arene compounds. Successful development of synthetic routes to various triynes and the subsequent cyclotrimerization key step gave systematic access to a variety of different
Winding up Alkynes: A Pd-Catalyzed Tandem-Domino Reaction to Chiral Biphenyls
作者:Markus Leibeling、Daniel B. Werz
DOI:10.1002/chem.201200175
日期:2012.5.14
Wrap it up! An intramolecular Pd‐catalyzed tandem‐domino process leading to highly sterically encumbered biphenyls is reported. The chirality of the newly formed axis is induced by the configuration of the carbohydrate backbone.