Synthesis of enantiomerically enriched allenes by (-)-sparteine-mediated lithiation of alkynyl carbamates.
[reaction: see text]. The alpha-deprotonation of alkynyl carbamates 3 with the chiral base (-)-sparteine (4)/n-butyllithium, transmetalation with ClTi(O(i)()Pr)3, and subsequent substitution with an aldehyde results in the formation of enantioenriched 4-hydroxyallenyl carbamates 11. Stereoselection is determined by dynamic resolution of the lithium/(-)-sparteine complexes by selective crystallization.
Schultz-Fademrecht
C
C
Organisch-Chemisches Institut, Westfälische Wilhelms-Universität Münster, Corrensstrasse 40, D-48149 Münster, Germany.
Wibbeling
B
B
Fröhlich
R
R
Hoppe
D
D
D000447:Aldehydes / Q000737:chemistry*; D000466:Alkadienes / Q000138:chemical synthesis*; D008094:Lithium / Q000737:chemistry*; D008956:Models, Chemical; D008958:Models, Molecular; D013034:Sparteine / Q000737:chemistry*
D000447:Aldehydes; D000466:Alkadienes; D013034:Sparteine; C025947:propadiene; D008094:Lithium