Organocatalytic Asymmetric Mannich Cyclization of Hydroxylactams with Acetals: Total Syntheses of (−)-Epilupinine, (−)-Tashiromine, and (−)-Trachelanthamidine
作者:Dipankar Koley、Yarkali Krishna、Kyatham Srinivas、Afsar Ali Khan、Ruchir Kant
DOI:10.1002/anie.201407185
日期:2014.11.24
cyclization between a hydroxylactam and acetal is described to provide fused, bicyclic alkaloids bearing a bridgehead N atom. Both aliphatic and aromatic substrates were used in this transformation to furnish chiral pyrrolizidinone, indolizidinone, and quinolizidinone derivatives in up to 89 % yield and 97 % ee. The total syntheses of (−)‐epilupinine, (−)‐tashiromine, and (−)‐trachelanthamidine also
Enantioselective Aza-Sakurai Cyclizations: Dual Role of Thiourea as H-Bond Donor and Lewis Base
作者:Yongho Park、Corinna S. Schindler、Eric N. Jacobsen
DOI:10.1021/jacs.6b09736
日期:2016.11.16
An enantioselective, catalytic aza-Sakurai cyclization of chlorolactams has been developed as an efficient entry into indolizidine and quinolizidine frameworks. Structure-enantioselectivity relationship studies and mechanistic analysis point to a dual role of the catalyst wherein the thiourea moiety of the catalyst is engaged in both anion binding and Lewis base activation of a substrate.