Gold(I) and Platinum(II)-Catalyzed Hydrofunctionalization of Allenes and Alkenes with Carbon and Nitrogen Nucleophiles
<p>The wide-spread occurrence of biologically active nitrogen-containing heterocycles and allylic amines inspired us to develop atom-economical methods for their syntheses.</p>
<p>A cationic gold(I) <italic>N</italic>-heterocyclic carbene complex catalyzed the intermolecular hydroarylation of allenes with indoles to form (<italic>E</italic>)-allylic indoles in modest to good yield at room temperature. The protocol was effective for monosubstituted, 1,3-disubstituted, and tetrasubstituted allenes and various indoles.</p>
<p>Platinum(II) bis(phosphine) complexes catalyzed the intermolecular hydroamination of monosubstituted allenes with secondary alkylamines in good yield with selective formation of (<italic>E</italic>)-allylic amines. The scope of the protocol included aryl and alkyl monosubstituted allenes as well as a variety of both cyclic and acyclic secondary alkylamines.</p>
<p>The scope of gold(I)-catalyzed intermolecular hydroamination of 1-alkenes with 1-methyl-2-imidazolidinone was expanded to include additional 1-alkenes functionalized with carboxylic acid derivatives. However, a nucleophile screen failed to identify nucleophiles other than cyclic ureas and 2-oxazolidinone that efficiently undergo hydroamination with 1-alkenes. Various carbamates, arylamines, amide derivatives, sulfur-containing amide derivatives, and α-heteroatom compounds failed to react with 1-octene under gold(I)-catalyzed conditions.</p>
<p>A chiral bis(gold) phosphine complex catalyzed the stereoconvergent, intermolecular enantioselective hydroamination of chiral, racemic 1,3-disubstituted allenes with carbamates to form <italic>N</italic>-allylic carbamates in good to high yield with up to 92% <italic>ee</italic>. In addition, enantiopurity experiments suggested the nature of the catalytically active species changes with increasing concentration of <italic>N</italic>-allylic carbamate.</p>
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