Baran Group Meeting
1/10/15
Organic Electron Donors
Julian Lo
1. Introduction
Organic electron donors (OEDs) are neutral, ground state organic molecules that reduce
substrates by single electron transfer.
Reactions with OEDs thus involve the intermediacy of radicals, which can ultimately end up
getting either reduced, converted into nucleophiles, or converted into electrophiles.
D •+ or
D 2+
D or
1D •+1
D •+
D
R–X
SET
SET
X–
R•
[R–X]•–
HAT
E+
R–
R–E
R–H
R–D +
D •+
Dr. William R. Dolbier, Jr.
University of Florida
Dr. John A. Muphy
University of Strathclyde
R–Nuc
Nuc –
Dr. Patrice Vanelle
Aix-Marseille University
Several reviews on OEDs as they pertain to organic synthesis have been recently published.
D
Comprehensive review: Vanelle, Angew. Chem. Int. Ed. 2014, 384
Additional review: Murphy, "Organic Electron Donors." In Encyclopedia of Radicals in
Chemistry, Biology, and Materials
Perspective on super electron donors: Murphy, J. Org. Chem. 2014, 3731
Perspective on super electron donors: Murphy, Chem. Commun. 2014, 6073
*Photoinduced electron transfer will be minimally covered, see "Photoinduced Electron
Transfer in the Days of Yore," Yan 2014 group meeting for more.
OEDs are typically electron rich alkenes, although there are some reports of aliphatic amines bearing weak OED properties. Shown below are some of the OEDs discussed along with their
corresponding redox potentials (E) and typical parent substrates for a qualitative reference.
Br
Cl
+N
I
MeBr
–3.5
E (V)
–3.0
–2.5
N
Me 2N
–1.5
–2.0
N
N
N
N
N
NMe 2
Murphy
E = –1.24 V
MeI
Murphy
E = –1.20 V
N
CBr4
–1.0
N
N
N
Me Me
Murphy
E1 = –0.82 V
E 2 = –0.76 V
2
–0.5
0.0
Me 2N
NMe 2
S
S
Me 2N
NMe 2
S
S
+0.5
Me
N H
N Ph
Me
TDAE
E1 = –0.78 V
E 2 = –0.61 V
TTF
E1 = +0.32 V
E 2 = +0.71 V
DMBI
E = +0.33 V
Me
N
1.0
N
Me
Me
Me
N
Me
nPr 3N
1,4 -DMP
E = +0.89 V E = +0.95 V
Baran Group Meeting
1/10/15
Organic Electron Donors
Julian Lo
2. Amines
3. Tetrathiafulvalene (TTF)
The reductive cleavage of halides from α-haloketones, esters, and acids using DBMI was initially
believed to proceed via Sn2 displacement with a hydride (Chikashita, J. Org. Chem. 1986, 540).
The first studies on TTF centered on its oxidation (Wudl, Chem. Commun. 1970, 1453).
O
Ph
O
DMBI
H
Br
THF, Δ
(89%)
Me
N H
N Ph
Ph
H
H
DMBI
N,N-dimethylaniline,
benzylamine also facilitate
facilitate similar reactions
Me
However, later experiments supported the intermediacy of radicals and led to the proposal of a
SET-initiated pathway (Tanner, J. Org. Chem. 1989, 3842).
The addition of radical
initiators/inhibitors
altered yields ca. ±50%
O
Ph
Also:
O
Cl
Ph
DMBI
Me
Ph
Me
Br
O
H
Ph
Me
Me
Me Me
N H
N Ph
Me
O
Me
N H
N Ph
Me
N
O
Br – Me
S
Ph
N
Br – Me
Ph
S
S
TTF •+ , deep purple solid
Similarly, solvent quantities of nPr 3N could facilitate SET to fragment PhSSPh (Ishibashi, Org.
Lett. 2009, 3298).
Me
Me
PhSSPh
PhSSPh
PhS
Me
TsHN
nPr 3N, H 2O
nPr 3N
Me
TsHN
140 °C
140 °C
SPh
(68%)
(45%)
O
O
S
CCl4
S+
S
+S
S
TTF 2+,
O
3a
R2
Mech?
O
-TTF
Br
1,4-DMP was proposed to dehalogenate trichloroacetamides through an analogous pathway
(Ishibashi, Tetrahedron Lett. 2008, 7771).
OAc
H
Reaction can still
H
OAc 1,4-DMP
Me proceed at 65 °C
(neat)
N
Cl
N
CCl 3
N
133 °C
N
Cl
DBU effects similar
Me
(52%)
reactivity at rt
O
O
1,4-DMP
Cl2
R1 R 2
O
Me
S
yellow solid
H 2O
-N2
-TTF•+
R1
TTF
SET
O
Me
N
S
S+
S
TTF facilitiated cyclizations of aryldiazonium salts via a radical-polar crossover mechanism
(Murphy, J. Chem. Soc. Perkin Trans. 1 1995, 623).
R2
R1
R1
OH
ROH and MeCN could also be
TTF
N 2+
2
used as nucleophiles, but others
R
acetone
(N 3-, HO-, malonate) were
H 2O
O
unsuitable (Murphy, Chem.
O
1
2
1a: R1 = R 2 = H
2b: R = Me, R = H, (73%) Commun. 1997, 1923).
1b: R1 = Me, R 2 = H
2c: R1 = R 2 = Me, (58%)
1c: R1 = R 2 = Me
S
S
N
Me
Me
S
Cl2
CCl4
S
S
TTF, yellow solid
Ph
Ph
Me
N H
N Ph
S
R1
R2
R2
R1
+TTF•+
S
O
O
S
NaN 3, acetone
S
N3
S
O
S
S
S
+
S
S
S
S
3a: R1 = R 2 = H, (75%)
(0.5 equiv)
The presence of heteroatom adjacent to the aryl group was required for termination by
nucleophilic substitution (Murphy, Chem. Commun. 2000, 627).
Cy
S
S
S
S
TTF
+
acetone
S
S
H 2O
N 2+ OMe
(48%)
(32%)
-TTF•+
-MeOH
+TTF•+
-N2
S
OMe
Cy
S
SRN1
+
OMe
This was used in total synthesis of aspidospermine (Murphy, J. Chem. Soc. Perkin Trans. 1
1999, 995).
NHCOCF 3
NHCOCF 3
NHCOCF 3
OH
O
TTF
Me
acetone
N
H 2O
N
N
H
H
(45%)
N 2+ Ms
Ms
Ms
N
N
N
Me
H
H
aspidospermine
N
H
Ms
N
H
Ms
Radical translocations via a [1,5]-HAT were also demonstrated (Murphy, J. Chem. Soc. Perkin
Trans. 1 1995, 1349).
Me
O
TTF
N
acetone
H
Me H 2O
N 2+ Me
N
Me
Me
O
N
H
Me
N
TTF
acetone
Me H 2O
O
Me
Me
O
H 2O
N
Me
H
Me
N
O
Me
S
+
TTF Me
N
O PhS
O
Me
Me
(14%)
PhS
OED
N 2+
OH
acetone
H 2O
O
4
O
5
O
S
Me
S
S
Me
E
N
S
S
Me
S
S
Me
E
S
TTF
4 (19%), 5 (48%)
TMTTF
4 (8%), 5 (67%)
Me
S
Br
N
N 2+ Ms
-N2
-TDAE•+
TDAE
DMF
(74%)
O
E
N
E
Me
DTDAF
4 (0%), 5 (72%)
N
TDAE
S O acetone
O
MeOH
N
Ms
Br
N
Ms
+
S
O
S
Bulking up the substitution around the TTF core led to a reduced rate of premature radical
trapping with TTF•+ and its derivatives (Murphy, Tetrahedron Lett. 1997, 7635).
TDAE had some illuminating properties (Pruett, J. Am. Chem. Soc. 1950, 3646).
Me 2N NMe 2
NMe 2
excess
Me 2N
NMe 2
F
F
O
O
NMe 2
Me 2NH
-hν
O
NMe 2
Me 2N
NMe 2
Me 2N
NMe 2
-TDAE
F
Cl
NMe 2
(2
equiv)
Me 2N NMe 2
"This was a clear, slightly yellow, mobile
liquid which was strongly luminescent in
"A small room can even be dimly lit for over
contact with air."
an hour... with about 10 mL of TDAE."
Can perform similar radical cyclizations to TTF, however, a leaving group typically needs to be
incorporated into the substrate to terminate the reaction since TDAE•+ does not recombine with
radical intermediates (Murphy, Beilstein J. Org. Chem. 2009, 1).
H
(85%)
O+
S
Me
Me S
(53%)
Me
N
H
Me
However, the DTDAFs were prone to rapid cleavage if DTDAF •+ trapped an intermediate
radical (Murphy, J. Chem. Soc. Perkin Trans 1 1999, 3637).
CO2Me
O
O
CO2Me
S
DTDAF
N 2+
N
acetone
Me
CHO
H 2O
(50%)
O
O
Mech?
4. Tetrakis(dimethylamino)ethylene (TDAE)
NCOCF 3
Me
N 2+ O
Baran Group Meeting
1/10/15
Organic Electron Donors
Julian Lo
N 2+
-Br•
+
N
H
(33%)
N
S O
O
(60%)
However, TDAE was initially used to dehalogenate polyhalogenated molecules with the more
electropositive halogens being easier to remove (Carpenter, J. Org. Chem. 1965, 3082).
-Cl –
CCl2
Cl
F 3C
Cl
F 3C
TDAE
Cl
TDAE
TDAE2+
+H+
BrCCl 3
CHCl 3 (22%)
–
–
Cl
pentane
decane
Br CCl 3
Cl
CF 3
CF 3 17 h
BrCCl
3
15 min
Cl
CCl 4 (31%)
(97%)
-BrCCl2 –
It has been suggested that TDAE performs two sequential SETs to acceptor substrates
to generate anions.
Me 2N
Baran Group Meeting
1/10/15
Organic Electron Donors
Julian Lo
NMe 2
Me 2N
NMe 2
R 3C–X
Me 2N
NMe 2 -20 °C
TDAE
Me 2N
SET
Me 2N X NMe 2
CR 3
~0 °C
NMe 2
+
–CR
3
Me 2N
NMe 2
TDAE 2+
Ph
Me
Me 2N
NMe 2
•+
TDAE
CR 3 + –X
charge transfer complex
Me 2N
NMe 2
+
–X
Br
SET
O
O
F
F
TDAE•+
O
F
F
PhCHO
TDAE
F
-Me2N –
O
O–
CF2Cl
O
O
N
O
Br
F
F
The initial products of the anionic additions could also undergo rearrangements (Vanelle,
Tetrahedron Lett. 2006, 6573).
via:
2-MePh
O
N
N
N
TDAE
Me
DMF
N
CCl 3
N
Cl
N
-20 °C to rt
O
Cl
(60%)
O
F
O
N
O
OH
-HF
Ph
O
(60%)
F F
O
N
CF2Cl
Ph
F
Me 2N O
N
DMF
-20 °C to rt
Radical intermediates could be intercepted using dihydrofuran as a radical trap.
N
Me
N
O
N
TDAE was used to generate HetCF 2 –, which could add into aldehydes, ketones (Médebielle,
J. Org. Chem. 1998, 5385), pyruvates, and thiocyanates (Médebielle, Synlett 2002, 1541
and Tetrahedron Lett. 2001, 3463).
CN
OEt
S
O
Ph
Ph
N
O
TDAE
N
N
+
Me
N
DMF
N
N
CHO
CF2Br
OH (ca. 55%
O
O
-20 °C to rt
for both)
NMe 2
(60%) F F
TDAE
(Hetero)aryl difluorochloromethyl ketones could also be added into activated electrophiles
such as aryl aldehydes, α-ketoesters, and thiocyanates (Médebielle, Tetrahedron Lett. 2008,
589; for more examples, see Dolbier J. Fluorine Chem. 2008, 930).
Ph
F F
Reductive cleavage of electron-deficient benzyl chlorides leads to adducts with α-halocarbonyl
compounds and other electrophiles (Vanelle, Tetrahedron 2009, 6128).
NO 2
O
Br
O
O
NO 2
O
TDAE
N
+
N
O
DMF
Cl
O
-20 °C to 70 °C
O
O
(68%)
Irraditation could increase yields in certain cases, but it altered the reaction outcome in other
ones (Vanelle, Eur. J. Med. Chem. 2010, 840).
NO 2
NO 2
NO 2
O
no hν
hν
N
N
+
N
2h
CO2Et 48 h
S
N
CO2Et
S
N
S
N
CO2Et
Cl
(51%)
(77%)
HO
from spontaneous E1 cb?
Sometimes light was believed to completely change the reaction mechanism (Vanelle,
Tetrahedron Lett. 2008, 1016).
Me
TDAE and Zn0 have similar reduction potentials, but offer different regioselectivities in vinylogous
Reformatsky reactions (Zhu, Tetrahedron Lett. 2004, 3677). Sulfonimine electrophiles only gave
modest selectivities (Zhu, Synlett 2006, 296).
OBn
OH OBn
OBn
O Zn0
TDAE
F
CO2Et
CO2Et
Br
CO2Et +
Ph
DMF
DMF
Ph
F
F F
F F
-10 °C to rt
0 °C
Ph
OH
(48%)
(95%)
OMe
Me
no hν
Me
Cl
Me
OMe
4-NO2Ph
no reaction
O
OMe
TDAE, DMF
-20 °C to rt
Me
hν
(82%)
Me
O
Me
OMe
Proposed SET to aldehyde:
O TDAE
R
hν
O
R
O
R
Ar
Cl
4-NO2Ph
O
OMe
Me
O2
Me
O
Me
OMe
R
TDAE can reduce CF 3I to CF 3–, which adds into various electrophiles (Dolbier, Org. Lett. 2001,
4271 and J. Fluorine Chem. 2008, 930).
O O
O
no h ν required:
S
S
TDAE (2.2 equiv)
O
O
O
N
p-tol
O
HO
CF
CF 3I (2.2 equiv)
3
(Het)Ar
DMF, hν
-20 °C to rt
R
R = H or Ph
(Het)Ar
Ar
R
Cl Ar
(48–98%)
(68–95%)
H
TDAE can be used as a reductant for transition metals, as demonstrated by the Pd-catalyzed
oxidative dimerization of (hetero)aryl bromides (Tanaka, J. Org. Chem. 2003, 3938).
S
S
N
DMF
0 °C to rt
CF 3–
Pd 0
PdIIBr
TDAE can reduce (CF 3S)2 to form a complex that can be used as a
J. Chem. Soc. Perkin Trans. 1 2000, 2183).
F 3CS SCF 3
TDAE
Me 2N
DME
-20 °C to rt
RSCF 3 + RS –
N
(200% based
on disulfide)
CF 3S –
NMe 2
DMF, MeCN
NMe 2 2CF3S- 0 °C to rt
(98%)
TDAE
Br cat. I 2
Br THF
67 °C
EtO 2C
SCF 3
SCF 3
or
(95%)
(80%)
Me
CO2Et
Ph
Br
MgSO 4
THF, 67 °C
O
Ph
Ph
(94%)
O
S
S+
MeCN
4-FPh -15 °C to rt
Ph
tBu
CO2Et
CO2Et
TDAE
Ar—Br
OHC
R
N
R
N
R
N
N
R
N
R
N
R
strongly
favored
Et Et
N
N
Exception when
R = Me or Et:
N
N
Et Et
6
Little is known about the redox chemistry of species like 6, but they can cleave P–Cl bonds to
form radicals (Goldwhite, J. Organomet. Chem. 1986, 21).
CO2Me
α-Bromoketones and esters could be dimerized using TDAE (Nishiyama, Tetrahedron Lett.
2006, 5565). Dithianyliums also underwent dimerization (Kirsch, J. Fluorine Chem. 2004, 1025).
TDAE
cat. I 2
-1
N
(51%)
O
TDAE2+
source (Kolomeitsev,
CO2Me
(32%)
Pd 0
A few other aliphatic tetraaminoethylenes are known, but most exist as their NHC monomers.
Reductive debromination in the presence of dienophiles can lead to the formation of Diels-Alder
adducts (Nishiyama, Tetrahedron Lett. 2005, 867).
Me
TDAE
TDAE can also be used for NHK
reactions substoichiometric in Cr
(Tanaka, Synlett 1999, 1930 and
Tetrahedron Lett. 2000, 81).
5. Bisimidazolidinylidenes
CF 3I
RSCF 3
PhCH 2Cl or
pyridine
NMe 2
OHC
RS–SR
CHO
OHC
DMF, 50 °C
(88%)
OHC
alkyl
(ca. 70%, (ca. 50% after
ca. 85:15 dr) hydrolysis)
SCF 3
TDAE (2.2 equiv)
CF 3I (5 equiv)
cat. PdCl 2(PhCN) 2
TDAE (2 equiv)
Br
The CF 3– could also be added into disulfides and diselenides (Dolbier, Org. Lett. 2004, 301).
N
Baran Group Meeting
1/10/15
Organic Electron Donors
Julian Lo
4-FPh
S
S
S
S
4-FPh
(91%)
P
Ph
P
Cl
Cl
6
Ph
(88%)
Cl
6
(57%)
P
Ph
Ph
P
tBu
Ph
tBu
P P
P P
tBu
6
Cl (1 equiv)
P
quant.
Cl
Ar = 2,4,6-tri(tBu)Ph
Ar
Cl
Ar
P
P
Ar
6
(excess)
Cl
quant.
Ar
tBu
Under irradiation, similar donors could reduce Ar3SiCl, Ar3GeCl, and Ar3SnCl to Ar3M•
(Lappert, J. Organomet. Chem. 1980, 5).
Mes Mes
+
Si
Mes
Cl
Me Me
N
N
N
N
Me Me
Mes
hν
Mes
Si
Mes
ESR only
P
P
Ar
Although 8 was unable to perform a second SET to form aryl anions, a more powerful SED
was identified that could (Murphy, Angew. Chem. Int. Ed. 2007, 5178).
6. Tetraazafulvalenes (TAFs)
Early studies on the redox potentials of bisimidazolium salts supported the notion that
introducing unsaturation into the rings of cyclic tetraaminoethylenes would result in strong
OEDs (see Vanelle, Angew. Chem. Int. Ed. 2014, 384).
N
N
N
N
Me Me
aromatic
+e –
N
N
+e –
-e –
N
N
Me Me
-e –
N
N
N
Me Me
nonaromatic
N
N
N
N
Me Me
–1.21 V
N
N
N
N
Me Me
–1.31 V
N
The TAF giving this dication
would have the highest
reduction potential
N
N
Me Me
–1.44 V
The earliest TAFs contained methylene bridges, which were essential in keeping the two NHC
halves dimerized (Murphy, Angew. Chem. Int. Ed. 2005, 1356).
2 I–
N
N
2 I–
N
KHMDS
PhMe
DMF
N
N
Me Me
7
N
I2
N
N
Me Me
8
N
N
N
N
Me Me
I
OMe 7, KHMDS
DMF, rt;
N
Ms
substrate
PhMe, Δ
OMe
N
Ms
not observed
N
Ms
(90%)
-MeO –
HAT
+e –
-I –
OMe
N
Ms
OMe
N
Ms
N
I
N
N
MeCN, Δ
0.003 M
24 days
OMe
+e –
N
Ms
2 I–
N
N
NaH
N
N
N
N
NH 3(l)
(98%)
N
N
2 e–
N
2 X–
N
N
N
9, (51%)
10
Cyclization supported the formation of an aryl anion, as aryl radicals do not add into esters.
Even polycyclic aryl bromides and chlorides could be reduced with 10.
O
I
H
CO2Et
10
CO2Et
Me
+
Me
Me
DMF
O
O Me
O
Me
Me
100 °C
(51%)
(21%)
Br
H
Cl
H
9, NaH
9, NaH
DMF, rt;
DMF, rt;
substrate
DMF, Δ
(86%)
substrate
DMF, Δ
(99%)
Unfortunately, much like with TTF, 10•+ could trap intermediate alkyl radicals and hydrolyze,
resulting in the formylation (Murphy, J. Am. Chem. Soc. 2009, 6475).
Me
Me
CHO
9, NaH
9, NaH
I
DMF, rt;
PhO
Br DMF, rt;
PhO
CHO
6
TAF 8 proved to be strong enough to reduce aryl iodides, which were previously unable to be
reduced by OEDs, making it the first "super electron donor" (SED).
I
N
N
Less planar salts were harder to reduce (shown with corresponding E in MeCN vs SCE):
N
Baran Group Meeting
1/10/15
Organic Electron Donors
Julian Lo
substrate;
HCl workup
6
substrate;
HCl workup
(13%)
N
Ms
(61%)
Proposed mechanism:
N
Ms
no deuteration
with d7-DMF
N
N
N
N
N
N
-H+
N
N
N
N
N
N
N
+H+
N
R
CH2R
10•+
O
O
H
R
R
-CO2
O
H
11
OH
R
H 3O+
N
N
R
N H N
N
N
R
Evidence against SET pathway involving 11:
Me
above
N
O
O
cond.
R
HO
R
H
R
N
(2%)
not formed
Me
Reductive cleavage of SO2Ph group from (di)sulfones and sulfonamides was possible with 10
(Murphy, J. Am. Chem. Soc. 2007, 13368).
9, NaH
PhO 2S H
DMF, rt;
substrate
DMF, 110 °C
(96%)
9, NaH
DMF, rt;
N
substrate
Ts DMF, 110 °C
PhO 2S SO2Ph
7. Bispyridinylidenes
The previous SEDs were not amenable to analog production, but similar SED synthesis
strategies could be used to generate different scaffolds (Murphy, Org. Lett. 2008, 1227).
N
H
(91%)
Proposed mechanism (later radical clock experiments suggested fragmentation to
form aminyl radicals is favored in the case of sulfonamides):
R1
–SO Ar +
X
2
R1 +e –
R1
R2
–
–
+e
+e
ArO2S X
ArO2S X
R1
R1
R2
R2
+
+H
SO2Ar + –X
H X
R2
R2
N
N
N
N
N
N
N
N
Me Me
isolated
N
N
N
N
N
N
N
Me Me
not isolated
not isolated
isolated
However, it was found that mono- and even untethered species could be generated in situ that
showed SED reactivity (Murphy, Chem. Sci. 2012, 1675).
2 I–
N
N
N
N
Me Me
Me I –
N
N
Me
NaH
N
DMF
N
N
Me Me
NaH
DMF
N
N
N
NaH
N
Me 2N
12
(83%)
NMe 2
Me 2N
NMe 2
Me Me
N
N
Ph
O
H
(61%)
Me 2N
I
H/D
13
tBu (1.5 eq) tBu
tBu
DMF, rt
(D 2O)
(95%)
tBu
"even a surface hydroxyl group
on glass could catalyze [the
decomposition of these TAFs]"
NMe 2
13
CO2Et (1.5 eq)
Me
DMF, rt
O
Me
(95%)
O
O
Me
Me
tBu
It could even do some things that other SEDs couldn't (Murphy, Synlett 2008, 2132).
O
O
O
12, NaH
DMF;
Me
Me
Me
Ph
N
Ph
N
N
substrate
OMe
H
H
(94%)
N (81%)
Proposed mechanism:
O
O
O
O
Me
Ph
N
Me SET
Me
Me
R
N
R
N
R
N
H
OMe
OMe
OMe
100 °C, (77%)
R
O
13
I
tBu
-MeO –
(79%)
N
Bispyridinylidene 13 could do everything that the other SEDs could do, but better and had
the advantage of being more "bottleable."
O
I
N
NH 3(l)
Ph
N
N
N
Me Me
I–
2 I–
Attempts to prepare analogs of 10 showed that its double methylene bridge was essential
for stability (Chen, Angew. Chem. Int. Ed. Engl. 1996, 1011).
N
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1/10/15
Organic Electron Donors
Julian Lo
N
H
Me
O
+H+
R
N
Me
Me
O
SET
R
O
N
Me
Me
N
H
5 equiv 12, 100 °C, (43%)
Similarly, acyloin derivatives could be deoxygenated by 13 (Murphy, J. Org. Chem. 2009, 8713).
O
Ph
Ph
12, NaH
DMF;
Ph
substrate
OR R = Ms, (93%)
R = Ac, (98%)
R = Piv, (97%)
O
O
Ph
H
12, NaH
DMF;
O
Me
Ph
substrate
Me Me O
(86%) Ph
Basicity occasionally problematic
O
O
Me Me
S–O (instead of C–O) bond cleavage of alkyl triflates was also possible (Murphy, Org. Biomol.
Chem. 2012, 5807).
18 O-DMF Me 2N +
OR H 2O Me 2N
OR
OTf 13
OH
R OTf
H OH
DMF
H
18 O-DMF labeling
Ph
Ph
(91%)
disproved a pathway SET;
H 2O
Ph
OTf
HAT
N
Bn invoking C–O bond
cleavage by DMF
Tf
Me 2N
OR H 2O
ROH
Br
3 equiv 13
(84%)
not observed!
H H
100°C, (40%)
Once again, photoactivation (UV) of these SEDs enhances their strength (Murphy, Angew.
Chem. Int. Ed. 2012, 3673)...
Ph
Ph
13
(3
equiv),
DMF
Cl
H
no hν, 100 °C (0%)
with hν, rt (87%)
O
O
Which even allows for SET to ground state benzenes, raising the possibility of a future OED
Birch-type reduction.
-e –
cis:trans 98:2
cis:trans 70:30
(66%)
+e –
13, hν
(6%)
It was found that benzyl esters, ethers, and sulfonamides could be debenzylated by this
approach (Murphy, Angew. Chem. Int. Ed. 2013, 2239 and Angew. Chem. Int. Ed. 2014, 474).
O
Me
Et
O
O
nBu
OMe
O
Et
nBu
Me
MeO
N
Ms
Me
OMe
13 (3 equiv)
hν, DMF, 24 h
(91%)
HO
Baran Group Meeting
1/10/15
Organic Electron Donors
Julian Lo
OMe
13 (6 equiv)
hν, DMF, 72 h
(73%)
HO
Me
Me
Cy
Me
13 (6 equiv)
hν, DMF, 72 h
(80%)
H
N
Ms
Cy
Additionallly, π-stacking interactions between 13 and aryl groups in the substrates can lead to
chemoselectivities opposite of conventional reagents (Murphy, J. Am. Chem. Soc. 2013,
10934).
CO2Et
CO2Et
13, hν
DMF
Ph
H
CO2Et
Ph
CO2Et
Ph
+H+
(75%)
Ph
O
CO2Et
0
CO2Et Na
or K 0
OEt
CO2Et
Ph
H
CO2Et
CO2Et
CO2Et
O
Ph
OEt
CO2Et
+H+
Ph