Enantioselective Intramolecular Alkene Hydroaminations Catalyzed by Yttrium Complexes of Axially Chiral Bis(thiolate) Ligands

Abstract

[structure: see text] A yttrium(III) complex derived from proligand 7c has been shown to be a superior catalyst for enantioselective intramolecular alkene hydroaminations that provide cyclic amines with ee's ranging from 69% to 89%.

Recent developments in enantioselective yttrium-catalyzed transformations

“…In a early report, Livinghouse and Kim described enantioselectivities of up to 69% ee for the asymmetric intramolecular addition of secondary amines catalyzed with a chiral aminobis(thio)phenolate yttrium complex [40]. More recently, Hannedouche and Schulz reported better enantioselectivities of up to 83% ee as the highest values achieved to date in such reactions catalyzed with chiral rare earth metal complexes [41].…”

“…On the other hand, the more facilitated asymmetric catalytic cyclization of alkylaryldisubstituted aminoalkenes 29d-h into the corresponding chiral pyrrolidines 30d-h was described with several types of chiral yttrium catalysts. For example, early in 2005, chiral aminobis(thio)phenolate yttrium complexes were employed for the first time in these reactions by Kim and Livinghouse, providing chiral pyrrolidines with enantioselectivities of up to 82% ee [40]. Later, preformed chiral yttrium catalyst 11 derived from sterically demanding (R)-N,N'-dibenzosuberyl-1,1'-binaphthyl-2,2'-diamine ligand was applied by Livinghouse et al to promote the asymmetric hydroamination of various alkylaryldisubstituted alkenes [25].…”

Asymmetric Hydroamination

“…Good to high enantioselectivities for a wide range of aminoalkene substrates, including internal olefins or secondary amines, were achieved using the aminothiophenolate catalyst system (R)-35 (Scheme 11.10), which was also obtained in situ [61]. Variation of the steric demand of the silyl substituent attached to the thiophenolate moiety allowed facile fine-tuning of the enantiomeric excess, resulting in increasing selectivity with increasing steric hindrance.…”

“…Scheme 11.10 Catalytic hydroamination/cyclization of aminoalkenes using chiral aminothiophenolate yttrium complexes[61].11.2 Hydroamination of Simple, Nonactivated Alkenes j353…”

Asymmetric Intermolecular Hydroamination of Unactivated Alkenes with Simple Amines

“…[4] Therefore, it is not too surprising that asymmetric hydroamination reactions [5] have been studied predominantly in intramolecular reactions. [6, 7] Intermolecular reactions have been reported only sporadically and all of these studies were limited to the reaction between aniline derivatives and activated alkenes, such as vinyl arenes, [8] 1,3-dienes, [9] and strained bicyclic alkenes.[10] The first enantioselective goldcatalyzed addition of cyclic ureas to unactivated alkenes in up to 78 % ee was reported recently by Widenhoefer and coworkers.[11] Herein we report the stereoselective addition of simple amines to unactivated alkenes utilizing chiral rareearth-metal-based catalysts.Catalyst systems based on rare-earth-metal complexes exhibit high catalytic activity, in particular in intramolecular hydroaminations, [2, 3f] whereas intermolecular hydroaminations are significantly more difficult to achieve as a result of the unfavorable competition between weakly coordinating alkenes and strongly coordinating amines. [4a,b, 6b, 12] We have previously reported on efficient biphenolate and binaphtholate rare-earth-metal catalysts, [6b, 13] which can catalyze the intramolecular hydroamination of aminoalkenes with high activity and up to 95 % ee.…”