PPh3/NaI driven photocatalytic decarboxylative radical cascade alkylarylation reaction of 2-isocyanobiaryls

Article abstract of DOI:10.1039/d0ra03211e

The first triphenylphosphine/sodium iodide driven photocatalytic decarboxylative cascade cyclization of 2-isocyano-biaryls with alkylN-hydroxyphthalimide (NHP) esters was developed. This operationally simple protocol results in multiple carbon-carbon bond formation under transition metal free conditions, affording a novel and environmentally benign entry to producing 6-alkyl phenanthridines with moderate to good yields.

Full text of DOI:10.1039/d0ra03211e

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PPh3/NaI driven photocatalytic decarboxylative
radical cascade alkylarylation reaction of
Cite this: RSC Adv., 2020, 10, 16510
2-isocyanobiaryls†
cd
Ketan Wadekar,‡ab Suraj Aswale‡c and Veera Reddy Yatham
*
The first triphenylphosphine/sodium iodide driven photocatalytic decarboxylative cascade cyclization of 2-
isocyano-biaryls with alkyl N-hydroxyphthalimide (NHP) esters was developed. This operationally simple
protocol results in multiple carbon–carbon bond formation under transition metal free conditions,
affording a novel and environmentally benign entry to producing 6-alkyl phenanthridines with moderate
to good yields.
Received 18th February 2020
Accepted 14th April 2020
DOI: 10.1039/d0ra03211e
rsc.li/rsc-advances
phenanthridine derivatives has gained signicant importance
in academic research. Recently, a cascade radical pathway
Introduction
involving radical addition to 2-isocyanobiaryls and subse-
quently intramolecular homolytic aromatic substitution has
been developed,9 which allows the rapid assembly of a phe-
nanthridine framework with high efficiency. In 2012, Chatani's
group disclosed Mn(III)-mediated radical cascade reaction of 2-
isocyanobiaryls with boronic acid under thermal conditions.10
Subsequently, several groups put their efforts for the construc-
tion of 6-substituted phenanthridines through the reaction of 2-
isocyanobiaryls with corresponding carbon radical precursors,
such as simple alkanes,11 alcohols,11a ethers,12 aldehydes,13 2-
bromide ethyl esters,14 aryl sulfonyl chlorides15 and 1,3-dicar-
bonyl compounds.16 Although these reported methods have
their own specic applications, but remains associated with
certain disadvantages such as employing metal catalysts, harsh
reaction condition and use of stoichiometric amounts of
oxidants. Very recently, few groups reported a metal-free
approach that utilizes aryl amines,17 carboxylic acids,18 hydra-
zines19 acyl peroxides,20 as a carbon radical precursor, which
appears to be an environmentally benign method for accessing
6-substituted phenanthridines. However, most of acyl perox-
ides, alkyl amines and hydrazenes are commercially unavail-
able. Thus, further new methodologies are quite desired for the
synthesis of 6-substituted phenanthridines.
Recently decarboxylative functionalization of alkyl N-
hydroxyphthalimide (NHP) esters in carbon–carbon bond
formation reactions have gained a signicant importance, as
they convert widely available and inexpensive chemicals into
valuable chemicals and reactive intermediates for synthesis.21
Photo decarboxylation of alkyl N-hydroxyphthalimide (NHP)
esters has been widely used for organic synthesis,22 as the
liberation of phthalimide and volatile CO2 as a by-products
indicates a strong driving force for the reaction, forming
versatile radical intermediates to build more valuable products.
Herein, we report the rst PPh3/NaI driven photocatalyzed
Visible-light photocatalysis has been widely recognized as
a powerful tool in organic synthesis to construct carbon–carbon
or carbon–heteroatom bonds.1 Through reactive intermediates
such as radicals and radical ions, unique reactions that are
previously inaccessible under thermal conditions can be
accessed. Signicant advances have been realized in this eld
by employing metal based catalysts2 or organic dyes3a–d as
photoredox catalysts. However, employing these metal based
photoredox catalysts has certain disadvantages: such as; they
are expensive, potentially toxic and limited availability.3e
Recently, visible light driven photoredox catalysis employing
inexpensive
chemicals
such
as
combination
of
triphenylphosphine/sodium iodide and CeCl3 emerged as
a robust alternative to generate radical entities under mild
reaction conditions.4 This approach replaces metal based pho-
tocatalysts by inexpensive catalysts, thus overcoming some of
the aforementioned problems.
Phenanthridine, a privileged structural core motif found in
natural products.5 Many synthetic phenanthridine derivatives
show bioactive and pharmaceutical properties, including anti-
tumoral, antibacterial, antiviral, cytotoxic, and DNA inhibitory
properties.6,7 In addition, phenanthridine derivatives reveal
signicant optoelectronic properties.8 Therefore, the develop-
ment of new and efficient methods for the preparation of
aDepartment of Organic Synthesis & Process Chemistry, CSIR-Indian Institute of
Chemical Technology, Hyderabad 500007, India
bAcademy of Scientic and Innovative Research (AcSIR), Ghaziabad 201002, India
cCSIR-Indian Institute of Chemical Technology, Hyderabad 500007, India
dSchool of Chemistry, Indian Institute of Science Education and Research,
Thiruvananthapuram 695551, India. E-mail: reddy@iisertvm.ac.in; reddy.iisc@
gmail.com
† Electronic supplementary information (ESI) available. See DOI:
10.1039/d0ra03211e
‡ Equally contributed to this work.
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decarboxylative cascade alkylarylation reaction of
2 iso-
cyanobiaryls in the presence of visible light irradiation at room
temperature.
Results and discussions
Inspired by the recent work of Shang and Fu (Fig. 1) who
developed photocatalytic decarboxylative alkylations mediated
by triphenylphosphine/sodium iodide,4d we wondered how
these activated carboxylic acids (1) would behave under similar
reaction conditions (Fig. 1) in presence of 2-isocyanobiaryls (2).
At rst, we chose 1a and 2a as model reactants to optimize the
reaction conditions for the desired decarboxylative radical
cascade alkylarylation using inexpensive PPh3/NaI as a photo-
catalyst. To our delight, when a solution of 1.5 equiv. of 1a with
1.0 equiv. of 2a in the presence of PPh3 (20 mol%) and NaI
(100 mol%) in acetonitrile was illuminated with a blue LED (455
nm) at 25 ꢀC for 24 h, product 3a was formed in 84% yield
(Fig. 2, entry 1). Replacement of NaI by KI also proceeded
smoothly to give product 3a in 80% yield (Fig. 2, entry 2). The
product formation 3a was slightly decreased upon employing
other iodide salts (Fig. 2, entries 3 and 4). Solvents such as
dimethylsulfoxide (DMSO) and dimethylformamide (DMF) in
place of MeCN afforded 3a in 65% and 60% yield respectively
(Fig. 2, entries 5 and 6). While solvents such as acetone, chlo-
roform (CHCl3) and EtOAc had a deleterious effect on the
reaction outcome (Fig. 2, entries 7–9). When triphenyl phos-
phine was replaced by other phosphines such as PCy3 and P(o-
tol)3, caused a drastic reduction in the yield of the reaction
(Fig. 2, entries 10 and 11). Substitution of PPh3 by other
nitrogen donors such as DMAP, Et3N observed trace amount of
product (Fig. 2, entries 12 and 13). Additionally, control exper-
iments conrmed that a catalytic amount of PPh3 and contin-
uous blue light irradiation were necessary for the reaction to
occur. Not even traces amount of 3a were observed in the
absence of light or the PPh3 (Fig. 2, entries 15 and 17).
Fig. 2 Optimization of the reaction conditions. 1a (0.3 mmol), 2a (0.2
mmol), PPh3 (20 mol%), NaI (100 mol%), CH3CN (3 mL) at 25 ꢀC,
455 nm LED for 24 h. [a]NMR yields using benzyl alcohol as internal
standard. [b]Isolated yield.
(1g) and ketone (1h) can be tolerated in our reaction conditions
to produce the corresponding 6-substituted phenanthridines
(3g and 3h) in 65% and 68% yield. Tertiary alkyl NHP esters
were smoothly converted to 6-alkyl phenanthridines in good
yields (3i–3k, 70–77%). Primary alkyl NHP-esters containing
variety of functional groups readily participated in this reaction
and gave corresponding 6-alkyl phenanthridines in good to
moderate yields. Primary alkyl NHP-esters derived from iso-
valeric acid, 4-phenyl buteric acid and 3-bromo-phenyl propo-
noic
acid
gave
the
corresponding
6-substituted
phenanthridines (3l–3n) in moderate yields (60–63%). Terminal
alkynes (1o) and alkenes (1p) are tolerated under these reaction
conditions gave the corresponding products 3o and 3p in 58%
and 56% yield. Also, primary alkyl NHP-esters (1q and 1r)
derived from 2-methoxy aceticacid and 4-oxopentanoic acid
were successfully converted to 6-alkyl phenanthridines 3q and
3r in moderate yields (57% and 56%).
Next, the scope of 2-isocyanobiaryls was examined. As shown
in Fig. 3, rst, the electronic variation at the para position of the
Ar2 ring was studied with NHP-esters (1a and 1i). Electron
withdrawing groups such as cyano, uoro, chloro, bromo, tri-
uoro methyl, triuoromethoxy groups were all well tolerated,
giving 6-substituted phenanthridines (3s–3x) in 50–65% yields.
Electron donating groups such as tbutyl, ethyl, methoxy gave
the corresponding 6-alkyl substituted phenanthridines (3y–3aa)
in 72–75% yields. Next ortho- and meta-substituted 2-isocyano
biphenyls were tested in our reaction conditions. In case of
ortho-phenyl substituted 2-isocyano biphenyl gave the corre-
sponding substituted phenanthridines (3ab) in 58% yield. In
case of meta-methyl substituted 2-isocyano biphenyl gave the
corresponding 6-alkyl phenanthridine (3ac) as a single regio-
isomer in 66% yield. In case of meta–para substituted 2-
With the optimized reaction conditions in our hand, we
survey the scope of the reaction. As shown in Fig. 3, a broad
range of alkyl NHP esters (1), reacted with 2-isocyanobiphenyl
(2a) providing the corresponding 6-alkyl phenanthridines in
good to moderate yields. Different types of secondary cyclic (1a–
1b) and acyclic (1c–1f) alkyl NHP esters participate in this
reaction to provide good yields (3a–3f, 67–78%). We were
pleased to nd that different functional groups such as amide
Fig. 1 Decarboxylative alkylations driven by PPh3/NaI photoredox
catalysis.
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Fig. 4 Preliminary mechanistic investigations; (Upper) radical clock
experiment; (Center) racemization of chiral alkyl NHP-ester; (Bottom)
plausible reaction mechanism.
mechanistic studies (Fig. 4). As anticipated ON/OFF experiment
indicated that our reaction required continuous blue light
irradiation to proceed (see ESI†). We currently believe that this
decarboxylative cascade cyclization reaction could proceed via
the generation of alkyl radicals. In a radical clock experiment
using alkyl NHP-ester (1s) derived from 2-cyclopropylacetic acid
under our reaction conditions, the ring-opened product 3p was
isolated (Fig. 4, upper). Moreover, secondary chiral alkyl NHP-
ester (1t) derived from enantiopure (S)-2-methylbutanoic acid
provided the racemic 6-alkyl substituted phenanthridines
product 3e (Fig. 4, center).
Based on these experimental observations and the report of
Rui Shang and Yao Fu et al.4d we propose that the decarbox-
ylative cascade cyclization reaction proceeds via formation of
charge transfer complex (CTC)23 (see ESI† for UV-visible
absorption spectra) between PPh3, NaI and NHP-ester (1a)
(Fig. 4).4d Aer photo fragmentation of this CTC complex
generates key alkyl radical I and PPh3-Ic. Subsequently, the
generated alkyl radical is added to 2-isocyanobiaryl 2, which
produce imine radical II that can form intermediate III through
an intramolecular radical cyclization. Further oxidation of III by
PPh3-Ic (Ered ¼ 0.69 vs. SCE)4d produces the corresponding car-
bocation IV and NaI, PPh3. The carbocation IV loses a proton
under reaction conditions to provide the desired product 3.
Fig.
3 Decarboxylative cascade alkylarylation reaction of 2-iso-
cyanobiaryls with alkyl NHP-esters. Reaction conditions as given in
Fig. 2 (entry 1). Isolated yields, average of at least two independent
runs. *regioisomer.
isocyano biphenyl gave the 6-alkyl phenanthridines (3ad) as
mixture of regio-isomers 65% yield. Dibenzothiofuran and
benzyloxy groups can be tolerated in our reaction conditions. In
case of 2-isocyano biphenyl containing dibenzothiofuran with
alkyl NHP-ester (1i) gave the 6-alkyl phenantharidine (3ae) in
57% yield. Finally, we tested one example of 2-isocyanobiphenyl
(2a) by introducing substitution on Ar1 ring was studied with
NHP-esters (1a) in our reaction conditions provided 6-alkyl
phenantharidine (3af) in 71% yield. Further, we have found that
Katritzky's N-cyclohexylpyridinium salt (4) and Togni's reagent
(5) can be activated by PPh3/NaI system to deliver 3a (75% yield)
and 6-triuoromethyl substituted phenanthridine (3ag) in good
yield (78% yield, see ESI†).
Conclusions
The efficiency of our photocatalytic decarboxylative radical
cascade cyclization leads us to conduct some preliminary
In summary, we have developed a general strategy for the
catalytic, radical decarboxylative cascade alkyl arylation of alkyl
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NHP-esters using an inexpensive PPh3/NaI system as a photo-
catalyst. This operationally simple protocol allows an efficient
synthesis of 6-substituted phenanthridines in moderate to good
yields under metal free conditions. Furthermore we showed
that in our photocatalytic conditions, different carbon radical
precursors can be activated to deliver 6-substituted
phenanthridines.
N. Yu, Q. An and Z. Zuo, J. Am. Chem. Soc., 2018, 140,
13580; (d) M.-C. Fu, R. Shang, B. Zhao, B. Wang and Y. Fu,
Science, 2019, 363, 1429; (e) A. Hossain, A. Vidyasagar,
C. Eichinger, C. Lankes, J. Phan, J. Rehbein and O. Reiser,
Angew. Chem., Int. Ed., 2018, 57, 8288; Angew. Chem., 2018,
¨
130, 8420; (f) V. R. Yatham, P. Bellotti and B. Konig, Chem.
¨
Commun., 2019, 55, 3489; (g) J. Schwarz and B. Konig,
Chem. Commun., 2019, 55, 486; (h) K. Zhang, L. Chang,
Q. An, X. Wang and Z. Zuo, J. Am. Chem. Soc., 2019, 141,
10556; (i) Y. Li, K. Zhou, Z. Wen, S. Cao, X. Shen, M. Lei
and L. Gong, J. Am. Chem. Soc., 2019, 141, 10556; (j) H. Yin,
P. J. Carroll, J. M. Anna and E. J. Schelter, J. Am. Chem.
Soc., 2015, 137, 9234; (k) Y. Qiao and E. J. Schelter, Acc.
Chem. Res., 2018, 51, 2926; (l) While this manuscript was
under preparation, R. Shang, Y. Fu et al. reported a related
methodology using PPh3/NaI as a photoredox catalyst:
Y.-T. Wang, M.-C. Fu, B. Zhao, R. Shang and Y. Fu, Chem.
Commun., 2020, 56, 2495.
Conflicts of interest
There are no conicts to declare.
Acknowledgements
V. R. Y. acknowledges SERB, New Delhi, for the nancial
support of Ramanujan Fellowship (SB/S2/RJN-138/2018). V. R.
Y. thanks to Dr Ch. Raji Reddy for his kind support. V. R. Y.
¨
thanks to Prof. Burkhard Konig for providing the blue LED set
up. V. R. Y thank to Dr Prathama S. Mainkar and Dr S. Chan-
drasekhar (Director, CSIR-IICT) for their kind support and
encouragement. CSIR-IICT Communication No. for this
manuscript is IICT/Pubs./2020/025.
5 (a) M. Suffnes and G. A. Cordell, The Alkaloids, Academic,
New York, 1985, vol. 25, p. 178; (b) T. Nakanishi,
M. Suzuki, A. Saimoto and T. J. Kabasawa, Nat. Prod., 1999,
62, 864; (c) T. Ishikawa, Med. Res. Rev., 2001, 21, 61; (d)
J. Hu, X. Shi, J. Chen, X. Mao, L. Zhu, L. Yu and J. Shi,
Food Chem., 2014, 148, 437.
6 (a) S. Simeon, J. L. Rios and A. Villar, Pharmazie, 1989, 44,
593; (b) S. D. Phillips and R. N. Castle, J. Heterocycl. Chem.,
1981, 18, 223.
Notes and references
1 For selected reviews on photoredox catalysis, see: (a)
¨
L. Marzo, S. K. Pagire, O. Reiser and B. Konig, Angew.
Chem., Int. Ed., 2018, 57, 10034; Angew. Chem., 2018, 130,
7 (a) O. B. Abdel-Halim, T. Morikawa, S. Ando, H. Matsuda and
M. Yoshikawa, J. Nat. Prod., 2004, 67, 1119; (b) L. Sripada,
J. A. Teske and A. Deiters, Org. Biomol. Chem., 2008, 6, 263.
8 (a) J. Zhang and J. R. Lakowicz, J. Phys. Chem. B, 2005, 109,
8701; (b) N. Stevens, N. O'Connor, H. Vishwasrao,
D. Samaroo, E. R. Kandel, D. L. Akins, C. M. Drain and
N. J. Turro, J. Am. Chem. Soc., 2008, 130, 7182.
9 Early examples of radical chemistry with isonitriles see; (a)
D. P. Curran and H. Liu, J. Am. Chem. Soc., 1992, 114, 5863;
(b) D. P. Curran, S.-B. Ko and H. Josien, Angew. Chem., Int.
Ed. Engl., 1995, 34, 2683; Angew. Chem., 2012, 107, 2948; (c)
D. Nanni, P. Pareschi, C. Rizzoli, P. Sgarabotto and
T. Tundo, Tetrahedron, 1995, 51, 9045; (d) B. Janza and
A. Studer, Org. Lett., 2006, 8, 1875For a recent review on
radical addition to biphenyl isonitrile see; (e) B. Zhang and
A. Studer, Chem. Soc. Rev., 2015, 44, 3505.
¨
¨
10188; (b) M. Karkas, J. Porco Jr and C. Stephenson, Chem.
Rev., 2016, 116, 9683; (c) N. A. Romero and D. A. Nicewicz,
Chem. Rev., 2016, 116, 10075; (d) K. Skubi, T. Blum and
T. Yoon, Chem. Rev., 2016, 116, 10035; (e) M. H. Shaw,
J. Twilton and D. W. C. MacMillan, J. Org. Chem., 2016, 81,
6898; (f) J. Twilton, C. C. Le, P. Zhang, M. H. Shaw,
R. W. Evans and D. W. C. MacMillan, Nat. Rev. Chem.,
2017, 1, 52; (g) Y. Xi, H. Yi and A. Lei, Org. Biomol. Chem.,
2013, 11, 2387.
2 For selected examples of Ir and Ru based photocatalysts see:
(a) Z. Zuo, D. Ahneman, L. Chu, J. Terrett, A. Doyle and
D. W. C. MacMillan, Science, 2014, 345, 437; (b)
A. Musacchio, L. Nguyen, G. Beard and R. Knowles, J. Am.
Chem. Soc., 2014, 136, 12217; (c) J. Jeffrey, J. Terrett and
D. W. C. MacMillan, Science, 2015, 349, 1532; (d) J. Chu
and T. Rovis, Nature, 2016, 539, 272; (e) For other metals 10 M. Tobisu, K. Koh, T. Furukawa and N. Chatani, Angew.
like Cu, Zn, Ni, Cr, Co and Fe based photocatalytsts see
recent review; B. M. Hockin, C. Li, N. Robertson and
E. Zysman-Colman, Catal. Sci. Technol., 2019, 9, 889.
3 (a) D. A. Nicewicz and T. M. Nguyen, ACS Catal., 2014, 4, 355;
(b) N. A. Romero and D. A. Nicewicz, Chem. Rev., 2016, 116,
Chem., Int. Ed., 2012, 51, 11363; Angew. Chem., 2012, 124,
11525.
11 (a) Z. J. Li, F. H. Fan, J. Yang and Z. Q. Liu, Org. Lett., 2014, 16,
3396; (b) W. X. Sha, J. T. Yu, Y. Jiang, H. T. Yang and J. Cheng,
Chem. Commun., 2014, 50, 9179; (c) Z. Q. Zhu, T. T. Wang,
P. Bai and Z. Z. Huang, Org. Biomol. Chem., 2014, 12, 5839.
¨
10075; (c) D. P. Hari and B. Konig, Chem. Commun., 2014,
50, 6688; (d) M. K. Bogdos, E. Pinard and J. A. Murphy, 12 (a) J. J. Cao, T. H. Zhu, S. Y. Wang, Z. Y. Gu, X. Wang and
Beilstein J. Org. Chem., 2018, 14, 2035; (e) M. Neumann,
X. S. J. Ji, Chem. Commun., 2014, 50, 6439; (b) L. Wang,
W. Sha, Q. Dai, X. Feng, W. Wu, H. Peng, B. Chen and
J. Cheng, Org. Lett., 2014, 16, 2088.
¨
¨
S. Fuldner, B. Konig and K. Zeitler, Angew. Chem., Int. Ed.,
2011, 50, 951; Angew. Chem., 2011, 123, 981.
4 (a) A. Hu, J.-J. Guo, H. Pan, H. Tang, Z. Gao and Z. Zuo, J. Am. 13 D. Leifert, C. G. Daniliuc and A. Studer, Org. Lett., 2013, 15,
Chem. Soc., 2018, 140, 1612; (b) A. Hu, J.-J. Guo, H. Pan and
Z. Zuo, Science, 2018, 361, 668; (c) A. Hu, Y. Chen, J.-J. Guo,
6286.
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14 H. Jiang, Y. Cheng, R. Wang, M. Zheng, Y. Zhang and S. Yu, 21 For a recent review on applications of NHP-esters in organic
Angew. Chem., Int. Ed., 2013, 52, 13289; Angew. Chem., 2013,
125, 13531.
15 L. Gu, C. Jin, J. Liu, H. Ding and B. Fan, Chem. Commun.,
2014, 50, 4643.
16 J. J. Cao, X. Wang, S. Y. Wang and S. J. Ji, Chem. Commun.,
2014, 50, 12892.
17 Z. H. Xia, J. B. Huang, Y. M. He, J. J. Zhao, J. Lei and Q. Zhu,
Org. Lett., 2014, 16, 2546.
synthesis see: S. Murarka, Adv. Synth. Catal., 2018, 360, 1735.
22 For applications of NHP-esters in photo induced reactions
see: (a) K. Okada, K. Okamoto, N. Morita, K. Okubo and
M. Oda, J. Am. Chem. Soc., 1991, 113, 9401; (b)
G. L. Lackner, K. W. Quasdorf and L. E. Overman, J. Am.
Chem. Soc., 2013, 135, 15342; (c) C. Hu and Y. Chen, Org.
Chem. Front., 2015, 2, 1352; (d) L. Candish, M. Teders and
F. Glorius, J. Am. Chem. Soc., 2017, 139, 7440; (e)
A. Fawcett, J. Pradeilles, Y. Wang, T. Mutsuga, E. L. Myers
and V. K. Aggarwal, Science, 2017, 357, 283.
18 L. S. Lu, G. Yaling Gong and Z. Demin, J. Org. Chem., 2015,
80, 9336.
¨
19 T. B. Xiao, L. Y. Li, G. L. Lin, Q. L. Wang, P. Zhang, Z. W. Mao 23 (a) Y. Cheng, C. Muck-Lichtenfeld and A. Studer, J. Am.
and L. Zhou, Green Chem., 2014, 16, 2418.
20 P. Changduo, Z. Honglin, H. Jie, C. Yixiang and
Z. Chengjian, Chem. Commun., 2015, 51, 3786.
Chem. Soc., 2018, 140, 6221; (b) L. Candish, M. Teders and
F. Glorius, J. Am. Chem. Soc., 2017, 139, 7440.
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