tives based on cross-dehydrogenative coupling (CDC).8
However, a limitation of such methods is the challenge in
controlling the regioselectivity of the C-H bonds. Alterna-
tively, the carboxylic group of R-amino acids provides the
possibility for site-specific functionalization of an R-amino
acid skeleton using decarboxylative coupling reactions to
generate amine products. With this notion in mind, very
recently we have developed a C-C bond-forming reaction
based on a copper-catalyzed oxidative decarboxylative
coupling of sp3-hybridized carbons of R-amino acids.9
Despite the efficiency of the copper-catalyzed method in
alkynylation and indolation, the attachment of other com-
pounds such as naphthaol and phenols is not effective under
such reaction conditions. Thus, an alternative catalytic system
is desirable both to make the method even less expensive as
well as to extend the scope of this methodology, in particular,
to naphthols and phenols to generate novel aminonaphthol
ligands (ligands of our interests for asymmetric synthesis).10
Iron catalysis appears to provide many opportunities in this
regard, because iron compounds are generally nontoxic,
environmentally benign, cheap, and readily available (the
second most abundant metal in the earth crust). Also, there
are often complementary reactivities between copper and
iron. Recently, iron has been applied in the cross-coupling
of arenes with Grignard reagents,11-13 and bioactive natural
products14,15 have also been synthesized successfully via iron
catalysis. Very recently, Vogel also reported an iron-
catalyzed desulfinylative C-C cross-coupling reaction of
sulfonyl chlorides with Grignard reagents.16 To the best of
our knowledge, however, there have been no reports on the
decarboxylative coupling by iron catalysis. Herein, we report
an efficient and practical reaction system for the iron-
catalyzed Csp3-Csp2 decarboxylative coupling.
Initial experiments were performed using proline 1a, 1.5
equiv of ꢀ-naphthol (2a), and 1.5 equiv of tert-butyl peroxide
(4a), together with 10 mol % of FeCl2 as the catalyst in
toluene at 115 °C under argon overnight (Table 1, entry 1).
The desired tertiary amino-naphthol product 3a was obtained
in 70% yield. To improve the yield, different catalysts were
examined, and FeSO4 gave the best yield compared with
other iron catalysts (entries 3-5). The attempts with other
oxidants, such as dicumyl peroxide and TBHP (tBuOOH)
led to lower yields of the desired product (entries 7 and 8).
However, when racemic ligand trans-1,2-diaminocyclohex-
ane was used, excellent yields were obtained (entries 2 and
6). Later, it was found that the ratio of the starting materials
was important to obtain high yields of the product. When
1.0 equiv of ꢀ-naphthol (2a) and 1.5 equiv of proline 1a
were used, an excellent yield was obtained (entry 9). The
use of 1.2 equiv of proline 1a gave a slightly lower yield of
the aminonaphthol product (entry 10). If there was no iron
catalyst, only 31% yield was obtained (entry 11). And in all
cases, under the examined oxidative reaction conditions, only
a small amount of BINOL was formed (Table 1).
The efficient formation of coupling products prompted us
to study the reaction scope further. As shown in Table 2,
the bromine group on the ꢀ-naphthol was tolerated by the
iron-catalyzed reaction (entry 2). ꢀ-Naphthol bearing an
electron-donating group at the C6 and C7 positions reacted
smoothly to give the corresponding products in good yields
(entries 3 and 4). Meanwhile, the use of N-benzylproline
containing a chlorine substituient at the meta-position also
gave good results (enties 5-7). When R-amino acid 1c
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