The Remarkable Ability of Lithium Ion To Reverse the Stereoselectivity in the Conjugate Addition of Li[BuCuI] to a Chiral N-Crotonyl-2-oxazolidinone
摘要:
[GRAPHICS]The influence of lithium ions on the conjugate addition of the monoorganocuprate reagent, Li[BuCuI], to a chiral crotonate has been investigated. The results show that iodotrimethylsilane (TMSI) is crucial for the asymmetric conjugate addition of the copper reagent, but only in THF or when 12-crown-4 is used. The reaction is thought not to involve any halosilane in any critical steps in the organocopper mechanisms conducted in Et2O.
Diastereoselective addition of monoorganocuprates to a chiral fumarate: reaction development and synthesis of (−)-dihydroprotolichesterinic acid
作者:J. Caleb Hethcox、Charles S. Shanahan、Stephen F. Martin
DOI:10.1016/j.tet.2015.05.023
日期:2015.9
Recent studies of diastereoselective conjugate additions of monoorganocuprates, Li[RCuI], to chiral γ-alkoxycrotonates and fumarates are disclosed. This methodology was applied to the shortest total synthesis of (−)-dihydroprotolichesterinic acid to date, but several attempts to prepare other succinate-derived natural products, such as pilocarpine and antrodin E, were unsuccessful.
Diastereoselective conjugate additions to different α,β-unsaturated N-acyl oxazolidinones using various monoorganocuprate reagents, Li[RCuI], are described. The TMSI activated conjugate addition reactions provided high yields (80–98%) and reversed major diastereomers (70–96% de) compared to the conventional copper(I)-promoted additions of Grignardreagents or the addition of Li[RCuI] to precomplexed MgBr2/imides