The Enantioselectivity and the Stereochemical Course of Copper-Catalyzed Intramolecular CH Insertions of Phenyliodonium Ylides

The Cu-catalyzed intramolecular CH insertion of phenyliodonium ylide 1b was investigated at 0° in the presence of several chiral ligands. Enantioselectivities varied in the range 38–72%, and were higher than those resulting from reaction of the diazo compound 1c at 65°. The intramolecular insertion of the enantiomerically pure methyl diazoacetate (R)-20 and of the corresponding phenyliodonium ylide (R)-21 proceeded to (R)-23 with retention of configuration with [Cu(hfa)2] (hfa=hexafluoroacetylacetone=1,1,1,5,5,5-hexafluoropentane-2,4-dione) and [Rh2(OAc)4]. These results are consistent with a carbenoid mechanism for the Cu-catalyzed insertion with phenyliodonium ylides. However, the insertion of the perfluorosulfonated phenyliodonium ylide (R)-29 afforded with [Cu(hfa)2] as well as with [Rh2(OAc)4] the cyclopentanone derivative 30 as a cis/trans mixture with only 56–67% enantiomeric excess.