L. Dechoux et al., A SIMPLE ONE-POT PREPARATION OF (Z)-CYCLOPROPANES FROM GAMMA,DELTA-KETOALKENES USING KOH DMSO INTRAMOLECULAR ALKYLATION CONDITIONS/, Tetrahedron letters, 34(46), 1993, pp. 7405-7408
Sequential treatment of gamma,delta-ketoalkenes with aqueous NBS in DM
SO and KOH as solid provides (Z)-cyclopropanes in good overall yields
with a diastereoselective excess >99%.