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 intermediates. A ring-closing olefin metathesis for the formation of the necessary allylsilane precursors highlights the initial route. The cyclopropanation step proceeds in good yield to provide exclusively trans-vinylcyclopropanes. Iteration of the sequence has provided an efficient route to bis-cyclopropanes. The stereospecificity of the second cyclization was shown to be dependent on distal functionality. An alternative approach produces these interesting structural units from skipped dienes in a single step.