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Lewis Acid‐Mediated Diastereoselective Reduction of N ‐Protected β‐Amino Ketones: Influence of the Nature of the Metal Atom and of the Nitrogen Protecting Group
Author(s) -
Bartoli Giuseppe,
Bartolacci Massimo,
Cortese Manuela,
Marcantoni Enrico,
Massaccesi Massimo,
Pela Roberto,
Sambri Letizia
Publication year - 2004
Publication title -
european journal of organic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.825
H-Index - 155
eISSN - 1099-0690
pISSN - 1434-193X
DOI - 10.1002/ejoc.200400016
Subject(s) - chemistry , diastereomer , lewis acids and bases , borohydride , protecting group , hydride , chelation , medicinal chemistry , metal , nitrogen atom , reducing agent , nitrogen , sodium borohydride , organic chemistry , stereochemistry , polymer chemistry , group (periodic table) , catalysis , alkyl
Lewis acid‐mediated chelation and non‐chelation control is one of the most fundamental and practical concepts in modern organic chemistry. Extension of these concepts to the reduction of different N ‐protected α‐substituted β‐amino ketones indicated that diastereoselectivity in the hydride addition step is strongly dependent on the nature of the metal atom and on the type of protecting group. Strongly chelating TiCl 4 and an electron‐rich nitrogen protecting group promoted the syn diastereoselectivity in noncoordinating solvents (CH 2 Cl 2 ) at −78 °C with BH 3 ·py as reducing agent. On the other hand, a Lewis acid as such as CeCl 3 and a bulky N ‐protecting group gave an excess of the anti ‐diastereomer in coordinating solvents (THF) at the same temperature with lithium borohydride (LiBH 4 ) as reducing agent. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)