= Solution
<Schwartz reagent> adds syn across the terminal <alkene>, placing <zirconium> at its terminal <carbon> and <hydrogen> at the substituted <carbon>. The organozirconium intermediate is \b[$\mathrm{PhCH(OMe)CH(Me)CH_2ZrCp_2Cl}$]. The two faces of the achiral starting <alkene> give enantiomeric organometallic intermediates.
Boron trifluoride coordinates the <ether> <oxygen>, making the benzylic C–OMe bond susceptible to cleavage. The C–Zr bond then transfers its <carbon> terminus intramolecularly to the benzylic <carbon> as the activated methoxy group departs, closing a cyclopropane. This can be represented as a concerted, strongly assisted displacement rather than requiring a freely equilibrating long-lived benzylic <carbocation>. <hydrozirconation> fixes the relative disposition of the new C–H and C–Zr bonds, and the preferred closure conformation places the bulky phenyl and methyl groups on opposite faces. The result is \b[racemic trans-1-methyl-2-phenylcyclopropane], with much less steric crowding than the cis alternative. The ring contains the original two <alkene> <carbons> and the original benzylic <carbon>; no carbene <carbon> is added.
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