Asymmetric cyclopropanations and cycloadditions of dioxocarbenes

Methods for enantioselective transfer of carbenes starting from precursors carrying two carbonyl groups have been elaborated. A one-pot procedure for olefin cyclopropanation with CH-acidic precursors via intermediate phenyliodonium ylides has been developed. The structure of the [Rh 2{(S)-nttl}4] catalyst was optimized to produce up to 98% ee in olefin cyclopropanations with dimethyl malonate or Meldrum's acid. Highly selective Rh(II)-catalyzed olefin cyclopropanations could be observed upon replacement of methyl diazoacetoacetate by methyl (silyloxyvinyl)diazoacetate. Enantioselective dipolar cycloadditions of diazopyruvate to polar olefins have been realized with Ru(II)-pybox catalysts. © Georg Thieme Verlag Stuttgart.