C O M M U N I C A T I O N S
Table 2. Rhodium-Catalyzed Intramolecular Hydroamination
Scheme 1
temp (
°
C)/
yields: aminea
(%)
entry
Ar
time (h)
enamineb (%)
1
2
3
4
5
6
Ph
80/24
80/24
70/48
80/24
80/24
80/72
76
78
83
78
82
71
4
1
1
3
3
trace
In closing, these rhodium-catalyzed reactions can be compared
to those of the same type of substrate in the presence of other
catalysts for hydroamination. Marks6 and Molander7 have reported
intramolecular hydroaminations of the parent substrate, but these
reactions formed pyrrolidines by Markovnikov addition of the NH
bond to the olefin. This regiochemistry for cyclization is, perhaps,
surprising because Marks6 has reported that intermolecular additions
of primary amines to vinylarenes occur to form the products from
anti-Markovnikov addition in the presence of lanthanocene catalysts.
Cyclizations of aminoolefins catalyzed by Pt(II) complexes also
give products from Markovnikov addition.4 Thus, the exclusive
formation of anti-Markovnikov products from the intramolecular
hydroamination catalyzed by [Rh(COD)(DPPB)]BF4 in this work
is particularly unusual. Studies to develop enantioselective versions
of these reactions and to understand the mechanism of these
processes are ongoing.
4-OMeC6H4
4-OMeC6H4
4-FC6H4
3,4-OMeC6H3
3,4-FC6H3
a Isolated yield. b Yield by H NMR spectroscopy.
1
Table 3. Stereoselective Rhodium-Catalyzed Intramolecular
Hydroamination
Acknowledgment. We thank the NIH Institutes of General
Medical Science (GM-55382) for support of this work. A.T. thanks
Mitsubishi Pharma Corporation for financial support.
Supporting Information Available: Reaction procedures and
characterization of reaction products. This material is available free of
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a Isolated yield. The ratio of cis/trans isomer is shown in parentheses.
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