Allylic Substitution for Construction of a Chiral
Quaternary Carbon Possessing an Aryl Group
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Abstract
Phenylcopper
reagents derived from 2:1 PhMgBr/Cu(acac)<sub>2</sub> and 3:1:1 PhMgBr/Cu(acac)<sub>2</sub>/ZnI<sub>2</sub> were found to be highly reactive and regioselective
in the allylic substitution of γ,γ-disubstituted secondary
allylic picolinates designed for construction of a quaternary carbon,
whereas the previous 2:1 ArMgBr/CuBr·Me<sub>2</sub>S reagent
and that with ZnX<sub>2</sub> were unsuccessful. The generality of
the ArMgBr/Cu(acac)<sub>2</sub> reagent was examined with enantiomerically
enriched allylic picolinates, which furnished quaternary carbons with
high efficiency in >92% regioselectivity and >97% chirality
transfer. Two cyclohexanes with a quaternary carbon were synthesized
by using these reagents
