conventional oxidants have proven compatible
with a majority of the aforementioned functional
groups. Substituents susceptible to nucleophilic
displacement by N3–, such as epoxide, ester, alkyl
chloride, and alkyl bromide (43b to 46b), were
also tolerated, likely as a result of the moderately
acidic reaction medium, which attenuates the
nucleophilicity of the azide anion. A representative
set of 11 alkene substrates was also examined
under constant-current conditions and exhibited
high Faradaic efficiencies (62 to 99%; fig. S1). Many
synthetic methods have been established for the
reduction of aliphatic azides to their corresponding amines with high functional group tolerance
(table S1). Accordingly, we demonstrated that a
number of 1,2-diazides, including those bearing
reductively labile groups (31b, 33b, 39b, 40b,
and 46b), could be chemoselectively converted
to 1,2-diamines (Fig. 3C). The diazidation and
reduction procedures could be carried out consecutively without elaborate isolation of the intermediate, thereby constituting a general, safe, and
operationally simple method for vicinal diamine
The unusually broad substrate scope of the
alkene diazidation piqued our interest in elucidating its mechanism, particularly the roles of the
anode and Mn catalyst in regulating the generation and reactivity of radical intermediates.
Radical clock experiments confirmed the intermediacy of radical adduct I (Fig. 4A): (i)
trans-Stilbene and cis-stilbene were converted
to a pair of diastereomeric 1,2-diazides with
identical diastereomeric ratios, (ii) diene 47a
reacted through both diazidation and cyclization
to form pyrrolidine 47b, and (iii) cyclopropyl-substituted alkenes 48a and 49a underwent
ring opening after the first azidyl addition, furnishing 48b and 49b, respectively, as the major
products. The highly electron-deficient, dicarbonyl-substituted radical intermediate originating from
substrate 49a was trapped by MnIII–N3, the
putative active catalyst, to form the diazide in
synthetically useful yield, with no evidence of
side reactions involving the electrophilic carbon
radical (e.g, electroreduction, addition to alkene
49a, or hydrogen-atom abstraction from a labile
C–H bond in the reaction system).
We propose two plausible mechanisms for the
diazidation. In the first scenario (Fig. 1C), direct
oxidation of N3– to N3·, followed by its addition
to the alkene and subsequent azidyl transfer from
MnIII–N3, leads to the final product. Alternatively,
Mn-assisted delivery of both equivalents of N3· to
the olefin (Fig. 4B) completes diazidation. In either
case, we propose that the key group transfer agent,
MnIII–N3, forms through ligand exchange from
MnII–X (X, Br or OAc) to MnII–N3 and subse-
quent anodic oxidation. Voltammetric and spec-
trophotometric studies substantiated the dual
catalytic cycle shown in Fig. 4B. In MeCN, N3–
exhibited an irreversible oxidative wave at ~0.5 V,
which shifted positively to 0.84 V on the addition
of HOAc, owing to protonation. MnII alone dis-
played no redox features between 0 and 1.5 V, but
on the addition of N3– and HOAc, a series of ir-
reversible anodic events appeared with an onset
potential of ~0.5 V. We assigned these waves to
the oxidation of azide-bound MnII, because this
anionic ligand is known to stabilize the MnIII oxi-
dation state (46). Preliminary ultraviolet-visible
spectroscopy data (figs. S4 to S5) also suggested
that MnII–N3 formed when N3– and MnII were
mixed and was subsequently oxidized to MnIII–N3
at a cell potential of 2.3 V, with a characteristic
ligand-to-metal charge-transfer transition at
422 nm (46). Taken together, the data favor
predominance of Mn-assisted dual radical group
transfer over direct addition of anodically
generated N3· to the alkene. The unusual com-
bination of exceptional reactivity and excellent
chemoselectivity observed in this catalytic sys-
tem likely originated from the putative azidyl
transfer agent, MnIII–N3. In a manner reminis-
cent of metal-oxo radical chemistry (47), the
redox-active metal catalyst enabled the gen-
eration of an azidyl equivalent in a controlled
fashion as a Mn-bound complex, preserving
the radical character needed to induce C=C
p-bond homolysis while diminishing the high
propensity of N3· to undergo dimerization,
C–H or electron abstraction, and other side re-
actions. This feature, together with the granular
control of oxidizing potential granted by elec-
trochemistry, led to the broad substrate gener-
ality and high functional group compatibility of
We anticipate that this synthetic protocol
will enhance chemists’ access to a diverse array
of 1,2-diamines. From a broader perspective,
we envision that this catalytic electrochemical
strategy and the radical transformations that
it enables will prove widely applicable in both
modern synthetic chemistry and pharmaceutical
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The authors declare no competing financial interests. Complete
experimental and characterization data are provided in the
supplementary materials. Financial support was provided by
Cornell University. This study made use of the Cornell Center for
Materials Research Shared Facilities, supported by the NSF
MRSEC (Materials Research Science and Engineering Centers)
program (grant DMR-1120296), and a nuclear magnetic
resonance facility supported by the NSF (grant CHE-1531632).
G.S.S. is grateful for an NSF Graduate Fellowship (DGE-
1650441). We thank K. L. Carpenter and W. Hao for providing
substrates 19a and 43a, respectively; K. M. Lancaster for access
to an ultraviolet-visible spectrometer; and D. B. Collum and
B. Ganem for assistance with manuscript preparation. S.L., N.F.,
and G.S.S. are inventors on U.S. patent application 62/513,646
submitted by Cornell University that covers the electrochemical
Materials and Methods
Figs. S1 to S6
Tables S1 and S2
13 May 2017; accepted 11 July 2017