A Practical Synthesis of a γ-Secretase Inhibitor

A practical and scaleable synthesis of the γ-secretase inhibitor 1 is reported. The inhibitor consists of a
central trisubstituted cyclohexane core with appended propionic acid, 2,5-difluorophenyl, and 4-chlorophenylsulfonyl moieties. Two alternative synthetic strategies, proceeding by way of a common
disubstituted cyclohexanone derivative 5, were studied. In the preferred route, conjugate reduction of
acrylonitrile derivative 4 with L-Selectride configures the desired relative stereochemistry of the
cyclohexane core with >99.9:0.1 dr. A second strategy, based on catalyst-controlled hydrogenation of
racemic cyclohexene derivative 2, is more convergent but less diastereoselective (up to 75:25 dr). The
common cyclohexanone intermediate 5 was constructed by a regioselective Diels−Alder condensation
of a 1,1-disubstituted vinyl sulfone 6 with 2-trimethylsiloxybutadiene.