Glass Lake
 
Just above Timberline Falls sits Glass Lake in Rocky Mountain National Park (August 2007)
 

 

 

Garden of the Gods

 
"Siamese Twins" rock formation at Garden of the Gods in Colorado Springs (August 2007)
 


Research

 

Overview:
Our general interest is in the area of synthetic organic chemistry, particularly the development of novel methodologies and their application in the synthesis of natural products exhibiting unique chemical complexity and significant biological activity.  Our recent focus is on synthetic challenges such as installation of various heteroatoms, creation of carbon-carbon bonds, and generation of polycyclic systems with an emphasis on chemo-, regio-, enantio-, and diastereoselectivity.  The following projects highlight some of our group's recent endeavors.

 

Epoxidation

 

 



Aziridination

Main

 



Diamination

 



Cyclopropanation

 

Diamination:
Vicinal diamines are present in many biologically active compounds (Figure 1).  Diamination of a carbon-carbon double bond presents an attractive strategy for the selective synthesis of vicinal diamines. We are currently exploring diamination methods via metal-catalyzed activation of N-N bonds (Figure 2).

diamination applications

Figure 1

 

diamination cycle

Figure 2

Recently, we reported a Pd(0)- and a Cu(I)-catalyzed regio- and stereoselective diamination of conjugated dienes using di-tert-butyldiaziridinone as the nitrogen source. Interestingly, these two metals provide complimentary regioselectivities (Figure 3). In addition, high enantioselectivities have been achieved with Pd(0) and chiral ligands. Furthermore, we have shown that terminal olefins can be effectively diaminated at allylic and homoallylic carbons in good yields with high stereoselectivities via C-H activation (Figure 4). We are also expanding the diamination method to other classes of olefins and their synthetic applications.

diamination (Pd and Cu)

Figure 3

 

diamination (C-H activation) 

Figure 4

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Aziridination:
In continuing our efforts towards small ring synthesis originating from carbon-carbon double bonds, we have developed amine catalyzed aziridinations of electron deficient olefins to form unprotected aziridines (Figure 5).  Our goals include designing more effective amine catalysts, development of an asymmetric process, expansion of substrate scope, and investigation of synthetic applications.

aziridination cycle

Figure 5

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Cyclopropanation:
Cyclopropanes are contained in many biologically and medicinally important molecules (Figure 6). Moreover, their ring strain allows for interesting synthetic transformations. The Simmons-Smith reaction is a widely utilized method for cyclopropantion of olefins. Recently, we have
developed a novel class of reagents (RXZnCH2I) that are highly reactive toward various olefins which had previously been unreactive (Figure 7).  We further developed a catalytic asymmetric version of the Simmons-Smith cyclopropanation for unfunctionalized olefins, which has been a long-standing synthetic challenge (Figure 8). Studies in this area are ongoing.

cyclopropanation application

Figure 6

 

cyclopropanation scheme

Figure 7

 

cyclopropanation cycle

Figure 8

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Epoxidation:
Optically active epoxides are highly versatile intermediates for the synthesis of a variety of enantiomerically enriched complex molecules (example shown in Figure 9).  Asymmetric epoxidation of olefins provides a powerful approach to the synthesis of such epoxides. To this end, we have developed an efficient asymmetric epoxidation method for a variety of trans- and trisubstitued olefins using fructose-derived ketone 1 as catalyst and Oxone or hydrogen peroxide as oxidants (Figure 10).  High enantioselectivities (>90% ee) have been achieved in many cases. Similar results have also been obtained for more electron deficient olefins using diacetate ketone 2.  In addition, we have found that glucose-derived ketone 3 can give high enantioselectivities for the epoxidation of cis- and terminal olefins.  

Brevitoxin B

Figure 9

 

epoxidation catalysts

 

epoxidation cycle

Figure 10

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