Catalytic asymmetric allylic and homoallylic diamination of terminal olefins via formal C-H activation

Article abstract of DOI:10.1021/ja8027394

This paper describes a catalytic asymmetric diamination process for terminal olefins at allylic and homoallylic carbons via formal C-H activation using di-tert-butyldiaziridinone as nitrogen source with a catalyst generated from Pd₂(dba)₃ and chiral phosphorus amidite ligand. A wide variety of readily available terminal olefins can be effectively diaminated in good yields with high regio-, diastereo-, and enantioselectivities. Copyright

Full text of DOI:10.1021/ja8027394

Published on Web 06/13/2008
Catalytic Asymmetric Allylic and Homoallylic Diamination of Terminal Olefins
via Formal C-H Activation
Haifeng Du, Baoguo Zhao, and Yian Shi*
Department of Chemistry, Colorado State UniVersity, Fort Collins, Colorado 80523
Received April 14, 2008; E-mail: yian@lamar.colostate.edu
Metal-promoted diamination of olefins provides an effective
approach to the synthesis of vicinal diamines, which are present in
various biologically active molecules and are used as chiral control
elements in asymmetric synthesis.1 Various diamination systems
have been developed.1–7 Recently, we reported a Pd(0)-8,9 and
Cu(I)10-catalyzed regio- and stereoselective diamination of conju-
gated dienes and trienes using di-tert-butyldiaziridinone (2)11 as
Figure 1. The X-ray structure of 6.
nitrogen source. We have also shown that readily available terminal
Scheme 1
olefins can be diastereoselectively diaminated at allylic and ho-
moallylic carbons Via formal C-H activation with Pd(PPh3)4
(Scheme 1).12 Considering its synthetic potential, it is highly
desirable to develop an asymmetric process for this diamination.
Compared to asymmetric diamination of conjugated dienes as
reported earlier,9a the current formal C-H diamination requires a
catalyst system which will be able to effectively convert the terminal
Scheme 2
olefin into a conjugated diene in situ besides being enantioselective.
Herein we wish to report our preliminary progress on this subject.
Asymmetric C-H diamination was initially investigated using
1-hexene (4) as substrate with slow addition of di-tert-butyldiaz-
iridinone (2) at 65 °C (Scheme 2) using phosphorus amidite ligand
L1 (previously used for the asymmetric diamination of conjugated
dienes).9a Ligand L1 gave 92% ee for 1-hexene (4) but with
moderate conversion (Scheme 2). To search for more effective
ligands, various commercially available or easily prepared chiral
ligands13,14 were then examined for the diamination of 1-hexene
under the conditions shown in Scheme 2. Studies show that
conversions and ee’s of the diamination were highly dependent on
the ligands used (Supporting Information). Overall, H8-BINOL-
based phosphorus amidite ligand L2 gave the highest conversion
for the reaction. Studies show that the reaction conversion was
Scheme 3
significantly influenced by the Pd/ligand ratio with 1:2.2 being
optimal. 31P NMR studies also indicate that complexes with one
Pd and two ligands were formed regardless of the Pd/ligand ratio
(Supporting Information).
Asymmetric C-H diamination of various terminal olefins with
Pd2(dba)3 and L2 was investigated. As shown in Table 1, all the
diamination reactions occurred highly regio- and diastereoselectively
at allylic and homoallylic carbons of terminal olefins, giving
diamination products in good yields (50-85%) and high enanti-
oselectivities (89-94% ee) (Table 1, entries 1-10). The olefin
geometry for cis- and trans-1,5-undecadiene was maintained during
the reaction (Table 1, entries 7 and 8). Both (R)- and (S)-5-
(trimethylsiloxy)-1-hexene were also diaminated in good yields with
high diastereoselectivities (Table 1, entries 11 and 12), indicating
that the stereochemistry of diamination products was primarily
determined by the chiral catalyst, and the stereogenic center of the
substrate had only a small effect on diastereoselectivities. The
diamination product in entry 11 was desilylated. The absolute
configuration of the resulting alcohol (6) was determined to be
(2R,3S,4R) by its X-ray structure (Figure 1). When 1,9-decadiene
(7) was subjected to the diamination conditions (Scheme 3),
bisdiamination compound 8b was obtained in 60% yield and 99%
ee15 along with small amount of meso compound 8a.16 Treating
8b with CF3COOH, concd HCl, and 1 N aqueous NaOH led to the
formation of optically active tetraamine 9 in 75% yield. When the
reaction was carried out with 1,7-octadiene (10), compound 11 was
obtained as a single diastereomer in 48% yield and 95% ee15
(Scheme 4). Since the bisdiaminations in Schemes 3 and 4 involved
multiple transformations, a higher catalyst loading was needed.
In summary, a catalytic asymmetric allylic and homoallylic
diamination for a variety of readily available terminal olefins has
been successfully achieved using di-tert-butyldiaziridinone (2) as
9
8590 J. AM. CHEM. SOC. 2008, 130, 8590–8591
10.1021/ja8027394 CCC: $40.75
2008 American Chemical Society

C O M M U N I C A T I O N S
Table 1. Catalytic Asymmetric C-H Diamination of Terminal
four C-N bonds can be stereoselectively constructed in one step
by formally replacing four sp3 C-H bonds.17 Compared to the
asymmetric diamination of conjugated dienes, the current asym-
metric diamination uses readily available terminal olefins without
the need to prepare conjugated dienes. This advantage is even more
apparent in the cases of bisdiaminations where the stereoselective
preparation of sensitive conjugated tetraenes is not necessary.
Further development of a more effective asymmetric catalytic
process and expansion of the substrate scope as well as synthetic
application are currently underway.
Olefinsa
Acknowledgment. We are grateful for the generous financial
support from the Camille and Henry Dreyfus Foundation and the
General Medical Sciences of the National Institutes of Health
(GM083944-01).
Supporting Information Available: Experimental procedures,
ligand studies, characterizations, X-ray structures of L1, L2, and 6,
and data for determination of enantiomeric excess of diamination
products along with the NMR spectra of compounds. This material is
available free of charge via the Internet at http://pubs.acs.org.
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a All reactions were carried out with olefin (0.80 mmol), 2 (2.0
mmol, 2.5 equiv), Pd2(dba)3 (0.04 mmol), and ligand L2 (0.176 mmol)
at 65 °C for 6 h. b The structures represent only proposed absolute
configurations by analogy. c Isolated yield based on olefin. d The ee was
determined by chiral GC (Chiraldex B-DM column) unless otherwise
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after the removal of t-butyl groups. f The (R,R) configuration was
determined by comparing the optical rotation with the reported one (see
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column) after the removal of t-butyl groups. h The ratio was determined
by achiral GC (VA-5MS column). i The (2R,3S,4R) configuration was
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Scheme 4
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nitrogen source with a catalyst generated from Pd2(dba)3 and H8-
BINOL-derived phosphorus amidite ligand L2, giving diamination
products in good yields with high regio-, diastereo-, and enanti-
oselectivities. For substrates bearing two terminal double bonds,
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J. AM. CHEM. SOC. VOL. 130, NO. 27, 2008 8591