While asymmetric transition-metal catalysis has become a powerful method for constructing chiral products, a challenge in this field is the identification of the correct ligand for high selectivity. We report here a simple approach to chiral catalyst formation: coupling of an available pool of Brønsted acids, namely, amino acid derivatives, with tunable ligands on copper catalysts. This system can be used to generate many different chiral environments simply by changing the amino acid or ligand employed and provides a scaffold for rapid screening and identification of the correct combination for high enantioselectivity. The latter is illustrated in the copper-catalyzed alkynylation of imines in up to 99% ee.
Having the munchies: A mild palladium‐catalyzed method to activate the carbon–oxygen bond of α‐amidoethers has been developed and applied to carbonylation chemistry (see scheme). A münchnone intermediate is generated in situ and undergoes a 1,3‐dipolar cycloaddition with alkynes to give diversely substituted pyrroles.
A one-step method to assemble pyrroles from alpha,beta-unsaturated imines and acid chlorides has been developed. This reaction is mediated by triphenylphosphine, which eliminates phosphine oxide to allow cyclization. This reaction has been employed to access a diverse range of pyrroles via modulation of the two building blocks and applied as well to the synthesis of lukianol A.
A copper-catalyzed Petasis-type reaction of imines, acid chlorides, and organoboranes to form α-substituted amides is described. This reaction does not require the use of activated imines or the transfer of special units from the organoboranes and represent a useful generalization of the Petasis reaction.
Palladium-catalyzed Saegusa-Ito oxidation of trimethylsilyl enol ethers is possible using Oxone as a stoichiometric oxidant and sodium hydrogen phosphate as a buffer. Cyclic and acyclic enones as well as α,β-unsaturated aldehydes are obtained in good to excellent yields.
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