Nickel-catalyzed
additions of arylboronic acids to alkynes, followed by enantioselective
cyclizations of the alkenylnickel species onto tethered ketones or
enones, are reported. These reactions are reliant upon the formal anti-carbonickelation of the alkyne, which is postulated
to occur by the reversible E/Z isomerization
of an alkenylnickel species.
Herein is described a versatile and broad synergistic strategy for expansion of chemical space and the synthesis of valuable molecules (e.g. carbocycles and heterocycles), with up to three quaternary stereocenters, in a highly enantioselective fashion from simple alcohols (31 examples, 95:5 to >99.5:0.5 e.r.) using integrated heterogeneous metal/chiral amine multiple relay catalysis and air/O₂ as the terminal oxidant. A novel highly 1,4-selective heterogeneous metal/amine co-catalyzed hydrogenation of enals was also added to the relay catalysis sequences.
A new, highly efficient Lewis base catalyst for a practical enantio‐ and diastereoselective crotylation of unsaturated aldehydes with E‐ and Z‐crotyltrichlorosilanes has been developed. The method was employed as a key step in a novel asymmetric synthesis of bioactive serrulatane diterpene (−)‐elisabethadione. Other strategic reactions for setting up the stereogenic centers included anionic oxy‐Cope rearrangement and cationic cyclization. The synthetic route relies on simple, high yielding reactions and avoids use of protecting groups or chiral auxiliaries.
Scheme 1. Allylation with primary allylboron reagents.Scheme 2. Allylation with chiral secondary allyl boronates. ] We thank the Leverhulme Trust for the Research grant F00 261AD and LU for a studentship to C.A.I.-P. We also thank Prof. T. Kanger (Tallinn University of Technology) for access to the computational resources as part of a collaboration within COST-ORCA action CM0905.Supporting information for this article is available on the WWW under http://dx.
Porous organic polymers have prospects as functional substrates for catalysis, with quite different molecular properties from inorganic substrates. Here we disclose for the first time that porous palladium(II)-polyimines are excellent catalysts for cooperatively catalyzed and enantioselective cascade reactions. In synergy with a chiral amine co-catalyst, polysubstituted cyclopentenes and spirocyclic oxindoles, including the all-carbon quaternary stereocenter, were synthesized in high yields. High diastereo-and enantioselectivities were achieved for these dynamic kinetic asymmetric transformations (DYKAT) of enals with propargylic nucleophiles.
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