Oligocyclopropane structural units from cationic intermediates

[GRAPHICS] syn- and anti-bis-cyclopropanes have been efficiently prepared through two distinct routes via the trapping of cyclopropylcarbinyl cationic intermedia tes. A ring-closing olefin metathesis for the formation of the necessary al lylsilane precursors highlights the initial route. The cyclopropanation ste p proceeds in good yield to provide exclusively trans-vinylcyclopropanes. I teration of the sequence has provided an efficient route to bis-cyclopropan es. The stereospecificity of the second cyclization was shown to be depende nt on distal functionality. An alternative approach produces these interest ing structural units from skipped dienes in a single step.