A synthesis of (-)-tashiromine and formal synthesis of (+)-tashiromine utilizing a highly enantioselective pyrrole/cobaloxime π-cation cyclization
Cyclization of (5-N-pyrrolyl-2-hydroxypentyl)cobaloxime (13) proceeds by intramolecular electrophilic aromatic substitution of a cobaloxime π-cation onto the pyrrole ring to provide 6-exo cyclization product (14) in 95% yield. This cyclization is highly enantioselective. It is applied to a synthesis of highly enantioenriched (-)-tashiromine, (-)-21, and a formal synthesis of (+)-tashiromine.
Gage, Jennifer L.,Branchaud, Bruce P.
p. 7007 - 7010
(2007/10/03)
Pyrroles as Terminators in Cationic Cyclizations. The Preparation of 5,6,7,8-Tetrahydroindolizidines and 6,7,8,9-Tetrahydro-5H-pyrroloazepines
N-(Epoxyalkyl)pyrroles 8-13 are readily prepared either by direct pyrrole N-alkylation with either ω-iodo epoxides or ω-iodo-1,2-alkanediol acetonides followed by conversion to the corresponding epoxides.The cyclizations of these N-(epoxyalkyl)pyrroles were examined with a range of Lewis acids providing cyclized products 14 and 16-21 in moderate to excellent yields.The cyclization products 14, 16, and 20 are formally the products of "anti-Markovnikov" attack on the less substituted epoxide terminus.
Tanis, Steven P.,Raggon, Jeffrey W.
p. 819 - 827
(2007/10/02)
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