Stereochemistry of cyclopropane formation involving group IV organometallic complexes

The reaction of (Z)-HDC=CHCH(OCH3)C6H5 (1) with Cp2Zr(D)CI followed by BF3-OEt2 gave phenylcyclopropanes 3a and 3b, both having cis deuterium. This stereochemical outcome requires inversion of configuration at the carbon bound to zirconium and is consistent with a "W-shaped" transition state structure for cyclopropane formation. In a Kulinkovich hydroxycyclopropanation, trans-3-deutero-1-methylcis-2-phenyl-1-cyclopropanol (5) was formed stereospecifically from Ti(O-i-Pr)(4), ethyl acetate, EtMgBr, and trans-beta-deuterostyrene. This stereochemistry requires retention of configuration at the carbon bound to titanium and is consistent with frontside attack of the carbon-titanium bond on a carbonyl group coordinated to titanium. In a de Meijere cyclopropylamine synthesis, a 3:1 mixture of N,N-dimethyl-N-(trans-3-deuterotrans-2-phenylcyclopropyl)amine (6a) and N,N-dimethyl-N-(cis-3-deutero-cis-2-phenylcyclopropyl)amine (6b) was formed from Ti(O-i-Pr)(4), DMF, Grignard reagents, and trans-beta-deuterostyrene. This stereochemistry requires inversion of configuration at the carbon bound to titanium and is consistent with a W-shaped transition structure for ring closure.