Regioselective radical addition of 3-oxopropanenitriles with terminal dienes promoted by cerium(IV) ammonium nitrate and manganese(III) acetate

Article abstract of DOI:10.1080/00397911.2019.1611858

Radical addition of 3-oxopropanenitriles to 1,3-butadiene derivatives promoted by (NH₄)₂Ce(NO₂)₆ and Mn(OAc)₃ afforded 5-ethenyl-4,5-dihydrofuran-3-carbonitriles in low to good yields. These dihydrofu

Full text of DOI:10.1080/00397911.2019.1611858

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Regioselective radical addition of 3-
oxopropanenitriles with terminal dienes
promoted by cerium(IV) ammonium nitrate and
manganese(III) acetate
Bahadir Hocaoglu & Mehmet Yilmaz
To cite this article: Bahadir Hocaoglu & Mehmet Yilmaz (2019): Regioselective radical addition
of 3-oxopropanenitriles with terminal dienes promoted by cerium(IV) ammonium nitrate and
manganese(III) acetate, Synthetic Communications, DOI: 10.1080/00397911.2019.1611858
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https://doi.org/10.1080/00397911.2019.1611858
Regioselective radical addition of 3-oxopropanenitriles with
terminal dienes promoted by cerium(IV) ammonium nitrate
and manganese(III) acetate
Bahadir Hocaoglu and Mehmet Yilmaz
Department of Chemistry, Faculty of Arts and Sciences, Kocaeli University, TR-41380 Umuttepe,
Kocaeli-Turkey
ABSTRACT
ARTICLE HISTORY
Received 21 March 2019
Radical addition of 3-oxopropanenitriles to 1,3-butadiene derivatives
promoted by (NH4)2Ce(NO2)6 and Mn(OAc)3 afforded 5-ethenyl-4,5-
dihydrofuran-3-carbonitriles in low to good yields. These dihydrofur-
ans were characterised by IR, 1H-NMR, 13C-NMR and HRMS spectra.
All radical additions performed via CAN and Mn(OAc)3 were occurred
on the terminal double bond on dienes. A mechanism for the forma-
tion of the dihydrofurans was proposed.
KEYWORDS
Cerium(IV) ammonium
nitrate; dihydrofuran;
radical addition
GRAPHICAL ABSTRACT
Introduction
Substituted dihydrofurans are significant class of compounds, since they show a wide
range of biological activities and form the basic structure of many natural products and
medicinal important compounds.[1,2] Attention to synthesis of dihydrofurans obtained
by the radical addition of 1,3-dicarbonyls to alkenes mediated by transition metal salts
[3–8]
such as Mn(OAc)3
or (NH4)2Ce(NO2)6 (CAN)[9–12] has increased, due to commer-
cially available and easily synthesized starting materials can be utilized to alter complex
reactions in the synthesis of biologically active compounds.
Nishino et al first reported the mechanism and the reaction of acylacetonitriles with
alkenes in the presence of Mn(OAc)3.[13,14] Afterwards, we obtained poly functional 4,5-
dihydrofuran-carbonitriles by treatment of acylacetonitriles with alkenes and acrylamide
derivatives bearing thiophen-2-yl and furan-2-yl groups.[15–20] Moreover, we reported
that some 4,5-dihydrofuran-carbonitriles show antibacterial and antifungal activities.[21]
In addition of these studies, thus far, our research group has carried out radical
CONTACT Mehmet Yilmaz
mehmet.yilmaz@kocaeli.edu.tr
Department of Chemistry, Faculty of Arts and Sciences,
Kocaeli University, TR-41380 Umuttepe, Kocaeli, Turkey.
Supplemental data for this article can be accessed on the publisher’s website.
ß 2019 Taylor & Francis Group, LLC

2
B. HOCAOGLU AND M. YILMAZ
cyclization of various active methylene compounds with alkenes, alkynes, dienes and
acrylamide derivatives.[22–29] Mn(OAc)3 was usually employed as radical oxidant
in these reactions. However, very recently we performed an optimization study on the
radical addition of 3-oxopropanenitriles to alkenes using CAN in ethereal solvents,
resulting in dihydrofurans in high yields on mild condition by CAN/THF system.[30] In
the present study, we applied the mentioned method to the reactions of 3-oxopropane-
nitriles with conjugated dienes promoted CAN/THF and obtained 5-ethenyl-4,5-dihy-
drofuran-3-carbonitriles as regioselectively. Besides, a comparative study is presented by
using MAH and CAN as radical oxidants.
Results and discussions
All 3-oxopropanenitriles (except 1c) were prepared by treatment of suitable esters and
CH3CN in the presence of NaH/PhMe, according to the literature.[15–20,31] 3-Methyl-1-
phenyl-1,3-butadiene 2a[32,33] and 3-methyl-1-(2-thienyl)-1,3-butadiene 2b[34] were syn-
thesized by utilizing Wittig reaction of triphenylphosphoniummethyl bromide with ben-
zoylacetone and (E)-4-(2-thienyl)but-3-en-2-one, respectively (Scheme 1).
Moreover, 1,3-diphenyl-1,3-butadiene 2c was obtained from the Wittig reaction of
benzaldehyde and triphenyl(2-phenylallyl)phosphonium bromide which was prepared
from the reaction of 2-phenylallyl bromide and triphenylphosphine.[35–37] 2-Phenylallyl
bromide was obtained from allylic bromination of 2-phenylpropene by NBS in
[38–41]
CCl4
(Scheme 2). All dienes were freshly prepared before used in the radical add-
ition reactions.
All radical reactions between 3-oxopropanenitriles and conjugated dienes were per-
formed using Mn(OAc)3/AcOH and CAN/THF as single electron generator and all
results are displayed in Table 1 and Table 2.
As seen in Table 1, treatment of 3-phenyl-3-oxopropanenitrile 1a with 3-methyl-1-
phenyl-1,3-butadiene 2a in the presence of Mn(OAc)3/AcOH gave 5-ethenyl-4,5-dihy-
drofuran-3-carbonitrile 3a in 53% yield, whereas the product 3a was obtained in 75%
yield by using CAN/THF system. Similarly, radical addition of 4-Me-phenyl (1b) and 4-
Cl-phenyl (1c) substituted 3-oxopropanenitriles to diene 2a in the presence of CAN
formed corresponding dihydrofurans 3b (53%) and 3c (60%), respectively. In the reac-
tion of 3-(2-thienyl)-3-oxopropanenitrile 1d with diene 2a, yield of product 3d when
Scheme 1. Synthesis of dienes 2a and 2b.
Scheme 2. Synthesis of 1,3-diphenyl-1,3-butadiene 2c.

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3
employed Mn(OAc)3 (59%) was obtained more than when used CAN (40%) (Entry 4).
However, dihydrofurans 3e and 3f were produced from the radical addition of 3-
(2-furyl) (1e) and 3-(2-benzofuryl)-3-oxopropanenitriles (1f) to diene 2a promoted by
CAN, respectively. Also, dihydrofuran 3g (30%) was obtained in low yield by the reac-
tion of 4,4-dimethyl-3-oxopentanenitrile 1g and 2a.
When CAN was used as radical oxidant in the reaction of 3-oxopropanenitriles (1a,
1d, 1e) with 3-methyl-1-(thiophen-2-yl)-1,3-butadiene 2b, neither formed (isolable
product) any product nor trace dihydrofuran was observed in TLC (Entries 1–3, Table
2). However, we achieved to obtain dihydrofuran-3-carbonitriles 3h–3j in low yields by
the radical addition of diene 2b with 3-oxopropanenitriles (1a, 1e and 1d, respectively)
mediated by Mn(OAc)3 (Table 2). According to these results, it is clear that no (or any
trace of) product could be obtained when thiophen-2-yl group was substituted to either
3-oxopropanenitrile or diene.
Reaction of 1,3-diphenyl-1,3-butadiene 2c with 1a promoted by CAN in THF
afforded 4,5-dihydrofuran-3-carbonitrile 3k (82%) in a very good yield (Entry 4). Also,
Table 1. Synthesis of 5-ethenyl-4,5-dihydrofuran-3-carbonitriles (3a–3g).
Product and
Entry 3-oxopropanenitrile
diene
dihydrofuran
yield (%)a
3a, 75 (53)b
1
2
3
4
3b, 53
3c, 60
3d, 40 (59)b
3e, 61
5
3f, 58
3g, 30
6
7
aYield of isolated product based on the amount of diene.
bYields in the brackets were obtained by using Mn(OAc)3/AcOH, the other products were obtained by CAN.

4
B. HOCAOGLU AND M. YILMAZ
Table 2. Synthesis of 5-ethenyl-4,5-dihydrofuran-3-carbonitriles (3h–3o).
Product and
yield (%)a
Entry
3-oxopropanenitrile
diene
dihydrofuran
1
3h, -- (56)b
3i, -- (44)b
3j, -- (46)b
3k, 82
2
3
4
5
3l, -- (88)b
6
7
8
3m, 60
3n, 69
3o, 46
aYield of isolated product based on the amount of diene.
bYields in the brackets were obtained by using Mn(OAc)3/AcOH, the other products were obtained by CAN.
radical addition of 2-thienyl substituted 3-oxopropanenitrile 1d to diene 2c in the pres-
ence of Mn(OAc)3 in AcOH produced 3l in 88% yield. 2-Furyl (3m) and 2-benzofuryl
(3n) substituted 4,5-dihydrofurans were obtained in good yields by the reactions of 1e
and 1f with 2c promoted by CAN. Moreover, 4,5-dihydrofuran 3o (46%) was synthes-
ised in moderate yield.
The mechanism proposed for the radical addition of conjugated dienes 2a–2c with
3-oxopropanenitriles 1a–1g is illustrated in Scheme 3. According to this mechanism,
while Ceþ4 is reduced to Ceþ3 (or Mnþ3 is reduced to Mnþ2) an a-carbon radical

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5
Scheme 3. Proposed mechanism for the formation of 5-ethenyl-4,5-dihydrofuran-3-carboni-
triles (3a–o).
A is formed. Then, addition of the radical to the terminal double bond of the diene
2a forms an allylic radical intermediate B. The radical B is oxidized to the carbocat-
ion C by CAN (or Mn(OAc)3), followed by cyclization of D to give 5-(2-phenyl-
vinyl)-4,5-dihydrofuran E. All radical addition to the dienes occurred on the
terminal double bond of the dienes as regioselectively, other adduct products were
not observed.
Conclusion
To sum up, we firstly performed the radical addition of 3-oxopropanenitriles (1a–1g) to
conjugated dienes (2a–2c), leading to the formation of 5-ethenyl-4,5-dihydrofuran-3-
carbonitriles (3a–3o) in low to good yields. Mn(OAc)3 and CAN were comparatively
used as radical oxidant within the reactions. According to these results, we conclude
that Mn(OAc)3 can be used effectively in the reactions of 3-oxopropanenitriles with
dienes containing thiophen-2-yl group, on the other hand, CAN is rather efficient with
the ones excluding thiophen-2-yl containing dienes.
Experimental
3-(4-Chlorophenyl)-3-oxopropanenitrile and other reagents are commercially available
and were purchased as highest purity. Melting points were determined on an electro-
thermal capillary melting point apparatus. IR spectra (ATR) were obtained with a
1
Bruker Tensor-27 400–4000 cm–1 range with 2 cm–1 resolution. H NMR, 13C NMR,
spectra were recorded on a Bruker Avance DPX-400 MHz and Varian Oxford NMR300

6
B. HOCAOGLU AND M. YILMAZ
High performance Digital FT-NMR spectrophotometers. High Resolution Mass Time-
of-Flight (TOF) was measured on an Agilent 1200/6210 LC/MS spectrophotometer.
[Mn(OAc)3]ꢀ2H2O was prepared by electrochemically method according to the litera-
ture.[42] Thin-layer chromatography (TLC) was performed on Merck aluminum-packed
silica gel plates. Purification of the products was performed by column chromatography
on silica gel (Merck silica gel 60, 40–63 mm).
General procedure for conjugated dienes (2a–2c)
NaH (22 mmol, in 60% mineral oil) was added to a solution of methyltriphenylphos-
phonium bromide (21 mmol) (or triphenyl(2-phenylallyl)phosphonium bromide for
diene 2c) in anh. THF. This mixture was kept at 60ꢁ C for 2 h, and then the corre-
sponding ketone or aldehyde (20 mmol) was added dropwise under stirring and cooling
in ice maintaining the temperature between 0ꢁ and 5 ꢁC. The temperature was then rap-
idly raised to r.t. temperature for 5 h. The THF was then removed under pressure and
the residue was extracted with hexane (5 ꢂ 20 mL). The organic phase was dried
(Na2SO4) and concentrated, and the crude product purified by column chromatography
(hexane as eluent).
3-Methyl-1-phenyl-1,3-butadiene (2a)[32,33]
1H NMR (400MHz, CDCl3), dH 7.42 (d, J ¼ 7.2 Hz, 2H, arom. CH), 7.31 (t, J ¼ 7.6 Hz,
2H, arom. CH), 7.24 (t, J ¼ 7.6 Hz, 1H, arom. CH), 6.88 (d, J ¼ 16.0 Hz, 1H, Holef),
6.53 (d, J ¼ 16.0 Hz, 1H, Holef), 5.11 (s, 1H, Holef), 5.07 (s, 1H, Holef), 1.97 (s, 3H, Me).
3-Methyl-1-(thiophene-2-yl)-1,3-butadiene (2b)[34]
1H NMR (400MHz, CDCl3), dH 7.15 (d, J ¼ 4.4 Hz, 1H, arom. CH), 6.99–6.96 (m, 2H,
arom. CH), 6.71 (d, J ¼ 16.0 Hz, 1H, Holef), 6.65 (d, J ¼ 16.0 Hz, 1H, Holef), 5.08 (s, 1H,
Holef), 5.04 (s, 1H, Holef), 1.94 (s, 3H, Me).
1,3-Diphenyl-1,3-butadiene (2c)[35–37]
1H NMR (400MHz, CDCl3), dH 7.48 (d, J ¼ 6.4 Hz, 2H, arom. CH), 7.40–7.15 (m, 8H,
arom. CH), 6.63 (d, J ¼ 12.0 Hz, 1H, Holef), 6.36 (d, J ¼ 12.0 Hz, 1H, Holef), 5.54 (s, 1H,
Holef), 5.26 (s, 1H, Holef).
General procedure for synthesis of dihydrofurans using Mn(OAc)3
[Mn(OAc)3]ꢀ2H2O (2.5 mmol) in AcOH (10 mL) was heated under N2 to 80 ꢁC until it
dissolved. Thereafter, the soln. was cooled to 60 ꢁC, and a soln. of 3-oxopropanenitrile
(1.2 mmol) and conjugated diene (1 mmol) in AcOH (5 mL) was added. The reaction
was completed when the initial dark brown solution had disappeared (10–30 min).
Afterward, H2O (20 mL) was added and the mixture extracted with CHCl3 (3 ꢂ 20 mL).
The combined organic phase was neutralized with sat. NaHCO3 solution, dried

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7
(Na2SO4), concentrated and the crude product was purified by column chromatography
or preparative TLC (silica gel, hexane/AcOEt as eluent).
General procedure for synthesis of dihydrofurans using CAN
To a solution of 3-oxopropanenitrile (1 mmol) and diene (1.2 mmol) in THF (10 mL)
under N2, a mixture of CAN (2.5 mmol) and NaHCO3 (2.5 mmol) was added at 45 ꢁC.
The reaction was completed when the orange colour of CAN had disappeared
(10–30 min) or when the 3-oxopropanenitrile spot on TLC had completely vanished.
H2O was added to the solution and the mixture was extracted with CHCl3 (3 ꢂ 20 mL).
The combined organic phase was dried (Na2SO4) and concentrated and the crude prod-
uct purified by column chromatography (hexane:AcOEt (5:1) as eluent).
Acknowledgements
Authors thank to UNAM (Bilkent University) for HRMS spectra.
Funding
The authors are grateful to the Kocaeli University Science Research Foundation (BAP 2010/57)
for financial support.
ORCID
Mehmet Yilmaz
http://orcid.org/0000-0001-7179-4045
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