The catalytic asymmetric synthesis of stereochemically defined fluoro-phenylserines is reported. In the title reaction, when methyl isocyanoacetate is employed, the number of fluorine atoms in the phenyl ring of benzaldehyde controls stereochemical outcome of the reaction giving rise in the case of monofluorobenzaldehydes corresponding trans-oxazolines with more than 90% of both trans-selectivity and % ee, while in the case of polyfluorobenzaldehydes corresponding cis-oxazolines are formed as dominant isomers with high enantiometric excess (up to 63% of cis with 86-90% ee). In contrast to this, aldol reactions of isocyanoacetamide with fluoro-benzaldehydes provide dominant formation of trans-oxazolines (77-92% of trans with 80-94% ee) in all cases studied. The observed unusual stereodifferentiation in the reaction of methyl isocyanoacetate with polyfluorobenzaldehydes is rationalized on the basis of an electron donor-acceptor type attractive interaction between the polyfluorophenyl ring and the enolate oxygen.
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AcknowledgmenWt. e thankt heJSPS Foundation(J apan),M inistryo f EducationJ,a pan,for a Grant-in-Aid for ScientificR esearchU, eharaM emorialF oundationI,n ternationaSlc ienceF oundation(U 6M000, U6M200),I NTAS (Network9 3-799)f or partialf inanciasl upporot f this work.