Catalysis through Temporary Intramolecularity: Mechanistic Investigations on Aldehyde-Catalyzed Cope-type Hydroamination Lead to the Discovery of a More Efficient Tethering Catalyst
摘要:
Mechanistic investigations on the aldehyde-catalyzed intermolecular hydroamination of allylic amines using N-alkylhydroxylamines are presented. Under the reaction conditions, the presence of a specific aldehyde catalyst allows formation of a mixed aminal intermediate, which permits intramolecular Cope-type hydroamination. The reaction was determined to be first-order in both the aldehyde catalyst (alpha-benzyloxyacetaldehyde) and the allylic amine. However, the reaction displays an inverse order behavior in benzylhydroxylamine, which reveals a significant off-cycle pathway and highlights the importance of an aldehyde catalyst that promotes a reversible aminal formation. Kinetic isotope effect experiments suggest that hydroamination is the rate-limiting step of this catalytic cycle. Overall, these results enabled the elaboration of a more accurate catalytic cycle and led to the development of a more efficient catalytic system for alkene hydroamination. The use of 5-10 mol % of paraformaldehyde proved more effective than the use of 20 mol % of a-benzyloxyacetaldehyde, leading to high yields of intermolecular hydroamination products within 24 h at 30 degrees C.
A Catalytic Tethering Strategy: Simple Aldehydes Catalyze Intermolecular Alkene Hydroaminations
作者:Melissa J. MacDonald、Derek J. Schipper、Peter J. Ng、Joseph Moran、André M. Beauchemin
DOI:10.1021/ja208867g
日期:2011.12.21
Herein we describe a catalytic tethering strategy in which simplealdehyde precatalysts enable, through temporary intramolecularity, room-temperature intermolecular hydroamination reactivity and the synthesis of vicinal diamines. The catalyst allows the formation of a mixed aminal from an allylic amine and a hydroxylamine, resulting in a facile intramolecular hydroamination event. The promising enantioselectivities
Hydrogen Bonding Directed Intermolecular Cope-Type Hydroamination of Alkenes
作者:Shu-Bin Zhao、Eric Bilodeau、Valérie Lemieux、André M. Beauchemin
DOI:10.1021/ol3023177
日期:2012.10.5
Intermolecularhydroamination of unactivated alkenes represents a significant synthetic challenge. An efficient Cope-typehydroamination is achieved under mild conditions for reactions of N-alkylhydroxylamines with allylic amines, using hydrogen bonding to achieve increased reactivity and high regioselectivity. This approach provides a number of highly functionalized vicinal diamine motifs as Markovnikov