Organic Letters
Letter
a
rearrangement experiment with (1-(2-phenylcyclopropyl)-
vinyl)benzene (43) proceeded smoothly to deliver opened
aminofluoride (44a) in 39% yield (eq 2). Both experiments
strongly supported the existence of radical intermediates in this
Scheme 5. Substrate Scope of the Diamination Reaction
reaction. Interestingly, the addition of 3.0 equiv of H O
2
resulted in the formation of the aminohydroxylation product
(
44b) in 18% yield (eq 3). Consistent with this observation,
the Hammett studies (ρ = −0.948) of various p-substituted
styrenes revealed that a positive charge was likely built up
during the aminofluorination reaction (Scheme 3C).
On the basis of these experimental results and literature
precedence, the cobalt-catalyzed aminofluorination reaction of
alkenes featuring an amidyl radical transfer and a subsequent
RPC mechanism was proposed (Scheme 4). Accordingly, the
a
Reaction conditions: alkene (0.2 mmol, 1.0 equiv), NFSI (0.5 mmol,
2
.5 equiv),Co(salen) 9 (0.01 mmol, 5 mol %) and PPh (1.0 equiv) in
3
b
EtOAc (c = 0.2 M) at 60 °C for 10 h under a N atmosphere. Gram-
scale reaction.
2
reaction was initiated by an inner-sphere single-electron
transfer between the cobalt catalyst (A) and fluorosulfonamide
1
4,19
agent (B) to generate cobalt(III) fluoride (C)
and an
20
amidyl radical (D), respectively. The addition of this amidyl
radical (D) to alkene then gave rise to a carbon-centered
radical (E). Followed by a RPC process, a carbocation (or
L-menthol (61), diacetone-D-glucose (62), and epiandroster-
one (63) derivatives were also readily achieved.
21,22
Note that both cobalt-catalyzed aminofluorination and
diamination of simple styrenes could be conveniently achieved
under very simple reaction conditions. On the contrary, the
same transformations via copper catalysis typically required
complex reaction settings, including the use of co-catalysts and
additives. Therefore, a better functional compatibility could
be readily achieved with cobalt as the catalyst, as shown in this
work. In addition, investigation on the relatively less developed
cobalt catalysis in this kind of transformation might offer
opportunities for a novel reaction mechanism and asymmetric
catalysis.
partial positive charge) species (F)
underwent nucleophilic
substitution by fluoride (path a) to afford the desired
aminofluorination product (H) and, meanwhile, regenerated
the cobalt catalyst to turn over the catalytic cycle. Alternatively,
aminofluoride (H) could also be generated via a radical
transfer process (path b) between the alkyl radical (E) and
cobalt(III) fluoride (C).
Because N-fluorosulfonamides have been reported as the
competent diamination agents of alkenes, we were also
interested in the exploration of such a possibility. Interestingly,
9
,11
2
3
we found that the addition of 1.0 equiv of PPh completely
3
In summary, we have developed highly efficient cobalt-
catalyzed divergent aminofluorination and diamination of
styrenes. Further extension of these protocols and mechanistic
investigation are currently underway in our lab.
diverted the cobalt-catalyzed reaction of styrene and NFSI
from aminofluorination to diamination. Controlled experi-
ments confirmed that aminofluoride obtained above was not
the intermediate of this diamination reaction. Extensive
reaction condition optimization revealed Co(salen) complex
ASSOCIATED CONTENT
sı Supporting Information
9
to be the optimal catalyst, and commercially available NFSI
■
*
served as both a radical and nucleophilic nitrogen agent. In
addition, it was found that the inclusion of PPh was the major
3
factor in this switch of reactivity from aminofluorination to
diamination. Consistent with this observation, mixing of NFSI
Experimental procedures and characterization data for
and PPh readily generated nucleophilic benzenesulfonimide
3
2
2
3
+
3
24
Corresponding Author
Finally, this protocol was found to embrace a multitude of
para-, meta-, or ortho-substituted styrenes (45−57), 2-vinyl-
naphthalene (58), and indene (59) (Scheme 5). Gram-scale
preparation of the vicinal diamine derivative (46) was also
successful. Remarkably, efficient diamination of estrone (60),
■
Ke-Yin Ye − Key Laboratory of Molecule Synthesis and
Function Discovery (Fujian Province University), College of
Chemistry, Fuzhou University, Fuzhou, Fujian 350108,
4
069
Org. Lett. 2021, 23, 4067−4071
Guo, Peng
