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Preparation and properties of some prochiral and chiral precursors of S-3-(3-hydroxyphenyl)-1-propylpiperidine (S-3-PPP)

Various synthetic approaches to 2, 3-dehydro- and 3, 4-dehydro-1-propionylpiperidines 12, 13 and to their 1-propyl congeners 14, 15, -two pairs of unsaturated, regioisomeric precursor of S-(-)-3-PPP [S-(-)-3-hydroxyphenyl)-1-propylpiperidine, 20] were investigated. Compounds 12 and 13 were prepared by regioselective elimination of water in 11. Preparation of 14 and 15 by two different methods is described. The ratio of the E/Z isomers at the C(O)-N bond in 11-13 was determined by 13C-NMR, and separation of the enantiotopic 1H-NMR signals in the enentiomers of 18 and 19 was investigated with chiral shift reagent Eu(tfc)3. Hydrogenation of 15 was performed with five different Rh(I) catalytic complexes, affording the O-methyl-congener of 3-PPP 19. Complete conversion of 15 into 19 was only achieved at elevated temperature and/or pressure to give the R- or S-isomer with low enetioselectivity (7-18%e.e.).

prochiral and chiral precursors ; S-3-(3-hydroxyphenyl)-1-propylpiperidine (S-3-PPP)

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