Synthesis, including asymmetric synthesis, of 3-oxabicyclo[3.1.0]hexanes and bicyclo[3.1.0]hexanes by the 1,5-CH insertion of cyclopropylmagnesium carbenoids as the key reaction
give 3-oxabicyclo[3.1.0]hexanes or bicyclo[3.1.0]hexanes bearing an ether group at the 4-position in moderate to good yields. When this procedure was carried out starting with enantiopure dichloromethyl p-tolyl sulfoxide, enantiopure 3-oxabicyclo[3.1.0]hexanes were obtained in good overall yields. These procedures provide a good way for the synthesis, including asymmetric synthesis, of multisubstituted
via 1,5-C–H insertion of cyclopropylmagnesium carbenoids as a key step. 1-Chlorocyclopropyl p-tolyl sulfoxides with an N,N-disubstituted aminomethyl group on the cyclopropane ring were prepared from dichloromethyl p-tolyl sulfoxide, α,β-unsaturated carboxylic acid esters, primary amines, and alkyl halides. Treatment of the sulfoxides with i-PrMgCl generated cyclopropylmagnesium carbenoids, which were
followed by sulfoxide/magnesium exchange of the sulfoxides with i-PrMgCl led to the generation of the cyclopropylmagnesium carbenoids possessing a magnesium anilide moiety. Subsequent intramolecularnucleophilicsubstitution of the cyclopropylmagnesium carbenoids occurred in a 4-exo-tet manner to give the 2-azabicyclo[2.1.0]pentanes. The optically active 2-azabicyclo[2.1.0]pentane was synthesized using
carbanion of enantiopure dichloromethyl p-tolyl sulfoxide with α,β-unsaturated carbonylcompounds gave optically active 1-chlorocyclopropyl p-tolyl sulfoxides having a carbonyl group with high asymmetric induction from the sulfur chiral center. Reduction of the carbonyl group followed by treatment with Grignard reagent, the 1-chlorocyclopropyl p-tolyl sulfoxides resulted in the formation of enantiopure allenic
The treatment of enantiopure aryl dichloromethyl sulfoxides in THF with strong bases such as LDA, LiHMDS, NaHMDS, and KHMDS resulted in racemization of the sulfur stereogenic center of the sulfoxides even at 78 degrees C. The rate of the racemization was found to be dependent on the alkali metal of the bases used. This is the first example of the racemization of the sulfur stereogenic center of alpha-sulfinyl carbanions at low temperatures. (C) 2010 Elsevier Ltd. All rights reserved.