| Abstract
| - Phosphine and bidentate N−N ligands inhibit the Alder-ene-type cycloisomerization ofenynes catalyzed by Pt(II) and favor the alkoxycyclization process. The enantioselective Pt(II)-catalyzed alkoxycyclization has been studied in the presence of chiral mono- and bidentatephosphines, as well as chiral bidentate N−N ligands. Modest levels of enantioselection (upto 50% ee) have been obtained with Tol-BINAP as ligand. The alkoxycyclizations with acatalyst formed from [Au(L)Cl]/AgX proceed more readily, and up to 94% ee's have beenobtained using [(AuCl)2(Tol-BINAP)] (47) as the precatalyst. The X-ray crystal structuresof Au(I) complexes 47 and chloro-(R)-2-(tert-butylsulfenyl)-1-(diphenylphosphino)ferrocenegold(I) (39) show the AuCl fragments monocoordinated with the P centers of the chiralphosphine ligands.
- The methoxycyclization of 1,6-enynes with chiral Pt(II) or Au(I) catalysts proceeds with low enantioselectivity, although up to 94% ee has been obtained in the reaction of an enyne substituted at the alkyne with a phenyl group with a cationic catalyst formed in situ from [(AuCl)2(Tol-BINAP)] and AgSbF6.
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