skip to main content


Title: Effect of Additives in the Hydroamination/Cyclization of Aminoalkenes Catalyzed by a Binaphtholate Yttrium Catalyst
Abstract

A series of various solvents and additives were tested in enantioselective hydroamination/cyclization reactions of aminoalkenes catalyzed by a binaphtholate yttrium catalyst. The functional group tolerance of the catalyst and the influence on the reaction rate and enantioselectivity was studied. Some weakly coordinating polar solvents, such as Et2O, MTBE, and chlorobenzene led to slightly increased reaction rates compared to the less polar solvent benzene, presumably due to a better stabilization of the polar transition state. Stronger binding solvents and additives, such as THF, DMAP, pyrrolidine,n‐propylamine, and 1‐phenylethylamine, decrease the reaction rate and diminish the enantioselectivity of the hydroamination product. Some additives, such as THF, Et2O, MTBE, chloro‐ and bromobenzene, as well as (+)‐sparteine resulted in slightly higher enantioselectivities in the cyclization of the model substrateC‐(1‐allylcyclohexyl)methylamine, although this observation was not generally true for other aminoalkene substrates. The reaction rates and enantioselectivities were depressed in the presence of (−)‐sparteine using the (R)‐binaphtholate‐ligated catalyst. In case ofC‐(1‐allylcyclohexyl)methylamine, the enantioselectivity was switched from 76% ee favoring the (S)‐enantiomer of the hydroamination product when using (+)‐sparteine to 22% ee in favor of the (R)‐enantiomer when (−)‐sparteine was used. The rates of cyclization of aminoalkenes and the resulting enantioselectivities significantly depend on substrate concentration with the highest rate (13.6 h−1) and enantioselectivity (68% ee) observed in dilute conditions (0.05 M) compared to a concentrated solution (0.5 M, 5.0 h−1, 35% ee) for 2,2‐dimethylpent‐4‐enylamine. These observations indicate that the reaction mechanism is shifted in favor of a slower, less enantioselective catalytic cycle involving a higher coordinate species when higher substrate concentrations or stronger binding additives are present.

magnified image

 
more » « less
NSF-PAR ID:
10396414
Author(s) / Creator(s):
 ;  ;  
Publisher / Repository:
Wiley Blackwell (John Wiley & Sons)
Date Published:
Journal Name:
Advanced Synthesis & Catalysis
Volume:
365
Issue:
4
ISSN:
1615-4150
Page Range / eLocation ID:
p. 568-578
Format(s):
Medium: X
Sponsoring Org:
National Science Foundation
More Like this
  1. Abstract

    Enantioselective substrate directed Heck reactions are desirable for the stereoselective synthesis of complex molecules. However, due to the coordination requirements of both chiral ligands and directing groups, such methodologies are underdeveloped. We report herein the desymmetrization ofmeso(1R,2S)‐cyclohex‐4‐ene‐1,2‐diol in an enantioselective and substrate directed fashion. The method provides allcissubstituted highly functionalized chiral allylic alcohols in a complementary fashion to other Heck protocols.The products were obtained in high enantioselectivities (higher than 95% ee) and moderate to high yields (38–87%). The noncovalent interactions responsible for the directing effect were elucidated through computational examination of relevant minima and transition structures.

    magnified image

     
    more » « less
  2. Abstract

    The diastereodivergent synthesis of bridged 1,2,3,4‐tetrahydroisoquinoline derivatives has been achieved by using appropriate modularly designed organocatalysts (MDOs) that are self‐assembled in situ from amino acids and cinchona alkaloid derivatives. The domino Mannich/aza‐Michael/aldol reaction between (E)‐2‐[2‐(3‐aryl‐3‐oxoprop‐1‐en‐1‐yl)phenyl]acetaldehydes and ethyl or benzyl (E)‐2‐[(4‐methoxyphenyl)imino]acetates catalyzed by MDOs gives two different diastereomers of the desired bridged tetrahydroisoquinolines in good yields and excellent diastereoselectivities (up to 99:1 dr) and enantioselectivities (up to >99%ee). The diastereodivergence was achieved in the aldol reaction step.

    magnified image

     
    more » « less
  3. Abstract

    Reaction conditions for the palladium‐catalysed decarboxylative generation and regiodivergent prenylation of 2‐azaallyl anions to form either the branched or linear prenylated benzylic imines from prenyl 2,2‐diphenyl‐glycinate imines are reported. For certain substrates, formation of side products arising from a competitive elimination/protonation pathway could be reduced by the addition of various basic additives. The optimal basic additive and reaction concentration were found to be highly substrate dependent. Geranyl esters also proved to be viable substrates for the corresponding regiodivergent decarboxylative geranylation reactions. Preliminary efforts toward an enantioselective variant are also presented.

    magnified image

     
    more » « less
  4. Abstract

    Direct preparation of alkylated amide‐derivatives by cross‐coupling chemistry using sustainable protocols is challenging due to sensitivity of the amide functional group to reaction conditions. Herein, we report the synthesis of alkyl‐substituted amides by iron‐catalyzed C(sp2)−C(sp3) cross‐coupling of Grignard reagents with aryl chlorides. The products of these reactions are broadly used in the synthesis of pharmaceuticals, agrochemicals and other biologically‐active molecules. Furthermore, amides are used as versatile intermediates that can participate in the synthesis of valuable ketones and amines, providing access to motifs of broad synthetic interest. The reaction is characterized by its good substrate scope, tolerating a range of amide substitution, including sterically‐bulky, sensitive and readily modifiable amides. The reaction is compatible with challenging organometallics possessing β‐hydrogens, and proceeds under very mild, operationally‐simple conditions. Optimization of the catalyst system demonstrated the beneficial effect of O‐coordinating ligands on the cross‐coupling. The reaction was found to be fully chemoselective for the mono‐substitution at the less sterically‐hindered position. Mechanistic studies establish the order of reactivity and provide insight into the role of amide to control mono‐selectivity of the alkylation. The protocol provides the possibility for convenient access to alkyl‐amide structural building blocks using sustainable cross‐coupling conditions with high efficiency.

    magnified image

     
    more » « less
  5. Abstract

    Commercial gold nanoparticles supported on titanium dioxide (TiO2) were found to be a highly efficient catalyst for alkyne hydroamination. Terminal alkynes could easily undergo intermolecular hydroamination with low catalyst loadings (0.2 mol% Au) under solvent‐free conditions. Indoles were efficiently synthesized using microwave heating through intramolecular hydroamination.

    magnified image

     
    more » « less