“…The proportions of the functionalized products 13-21 were constant with the electrophiles, the metalating agent and the time and reflected the proportion of the starting material; this showed a similar behavior of the three compounds (10)(11)(12) with regard to the metalation reaction. The most important result was that the metalation of 11 was regioselective in ortho position relative to the fluorine atom, leading to the conclusion that the fluorine atom was a much better ortho-directing group than the chlorine atom in these series.…”
Section: Sep-oct 2003 855mentioning
confidence: 78%
“…The metalation of 2,6-dichloro-3-fluoropyridine [12] with n-butyl lithium was regioselective in ortho to the fluorine atom.…”
The regioselectivity of the metalation of 2‐chloro‐6‐methoxypyrazine, 2‐fluoro‐6‐methoxypyrazine and 3‐fluoro‐6‐chloropyridazine was studied; the relative ortho‐directing power was F > OMe > Cl.
“…The proportions of the functionalized products 13-21 were constant with the electrophiles, the metalating agent and the time and reflected the proportion of the starting material; this showed a similar behavior of the three compounds (10)(11)(12) with regard to the metalation reaction. The most important result was that the metalation of 11 was regioselective in ortho position relative to the fluorine atom, leading to the conclusion that the fluorine atom was a much better ortho-directing group than the chlorine atom in these series.…”
Section: Sep-oct 2003 855mentioning
confidence: 78%
“…The metalation of 2,6-dichloro-3-fluoropyridine [12] with n-butyl lithium was regioselective in ortho to the fluorine atom.…”
The regioselectivity of the metalation of 2‐chloro‐6‐methoxypyrazine, 2‐fluoro‐6‐methoxypyrazine and 3‐fluoro‐6‐chloropyridazine was studied; the relative ortho‐directing power was F > OMe > Cl.
“…On the other hand, a partial epimerization at the 2-position of the proline moiety could occur, as observed in the application of (S)-proline and 4-hydroxy-(S)-proline in coupling reactions, due to intermediate enolization. 28 We are presently developing an IL-tagged hydroxyproline derivative with a quaternary C-atom at the 2-position which cannot epimerize and will investigate its performance in recycling experiments.…”
Section: Excellent Diastereoselectivities and Ee Values Above 90%mentioning
Novel 1,2,3-triazolium-tagged proline derivatives were synthesized by copper-catalyzed click-reaction of alkynes with azides and N-alkylation of the resulting 1,2,3-triazoles. They were applied as recyclable organocatalysts in direct asymmetric aldol and Michael reactions with high enantioselectivity and diastereoselectivity. These catalysts performed better than (S)-proline itself; that is to say, a synergistic effect of the triazolium and the proline moiety exists. The reactions could be carried out either in conventional solvents or in ionic liquids. The catalysts were easily recycled and reused several times.
“…One stereoselective synthesis has been reported; Seebach found that pivaldehyde N , O -acetal alkylation (eq 2) cleanly afforded trans-isomer 6 (ds >95%) after hydrolysis. However, this route is limited by the availability of the trans- 4-hydroxyproline, − and does not allow access to the cis isomers.…”
To extend the memory of chirality (MOC) methodology to structurally more diverse compounds, the synthesis of 4-hydroxy-alpha-methylprolines was undertaken. Yield and selectivity were very good, with an unexpected reversal in selectivity observed for the cyclization of one adduct with an unprotected hydroxyl.
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