Synthesis of an ethynyl carbamate and application for enantioselective cyclocarbolithiation.
[reaction: see text] The intramolecular trans-cyclocarbolithiation of the alpha-lithiated 4-substituted 5-hexynyl carbamate (1S,4RS)-14 employing lithiodestannylation is presented. The 5-exo-dig cyclization products cis-/trans-16a were formed exclusively. The highly enantioenriched organotin precursor (S)-11 was synthesized via an asymmetric deprotonation of the corresponding alkyl carbamate 10 by the chiral complex sec-butyllithium/(-)-sparteine and subsequent substitution with tributyltin chloride.
Gralla
Gabriele
G
Organisch-Chemisches Institut, Westfälische Wilhelms-Universität Münster, Corrensstrasse 40, D-48149 Münster, Germany.
Wibbeling
Birgit
B
Hoppe
Dieter
D