1,2-Difluorobenzene is reacted with 3-chloropropionyl chloride to
produce 3-chloro-1-(3',4'-difluorophenyl)-propan-1-one, which is by
addition of N,N-dimethylformamide,
phloroglucinol and sodium iodide in the next step converted to
1-(3',4'-difluorophenyl)-3-nitro-propan-1-one. The keto group of the
latter intermediate is in the subsequent step stereochemically reduced
to hydroxyl group by the use of chiral oxazaborolidine together with
borane dimethyl sulfide or borane-N,N-diethyl aniline complex in the presence of tetrahydrofurane. The obtained (1R)-1-(3',4'-difluorophenyl)-3-nitro-propan-1-ol
is then added to a mixture of triphenylphosphine and
diethylazodicarboxylate in benzene to yield (1S,2R)-2-(3',4'-difluorophenyl)-1-nitrocyclopropane, which is in the last step converted to 2-(3,4-difluorophenyl)cyclopropane amine by reduction of the nitro group by catalytic hydrogenation with palladium catalyst and zink dust.
