Alkyl metal asymmetric reduction. Part IV. Reduction of isopropyl phenyl ketone by optically active dialkylzinc compounds: dependence of stereoselectivity on the distance of the chiral centre from the metal atom
The reaction between isopropyl phenyl ketone and optically active dialkylzinc compounds of general formula (Bus*[CH2]n)2Zn (n= 1, 2, or 3) leads to optically active 2-methyl-1-phenylpropan-1-ol, and the stereoselectivity of the reduction process is dependent on the distance of the chiral centre from the metal atom. The results are rationalized in terms of conformational requirements of the non-reacting groups which, determining the preferential transfer of one of the two β-hydrogen atoms to the metal atom, should control the stereoelectronic interactions among the reacting groups in the diastereoisomeric transition states.