Visible-light- induced aerobic dioxygenation of styrenes under metal- and additive-free ambient conditions

Article abstract of DOI:10.1016/j.tetlet.2016.12.073

Visible light promoted hydroperoxidation of styrenes using hydroxylamine and molecular oxygen from air under metal-free and additive-free conditions at room temperature is described. Hydroperoxides were further converted into corresponding hydroxy compoun

Full text of DOI:10.1016/j.tetlet.2016.12.073

Accepted Manuscript
Visible-light- induced aerobic dioxygenation of styrenes under metal- and ad-
ditive-free ambient conditions
Supravat Samanta, Chitrakar Ravi, Abhisek Joshi, Venkatanarayana Pappula,
Subbarayappa Adimurthy
PII:
S0040-4039(16)31729-4
DOI:
http://dx.doi.org/10.1016/j.tetlet.2016.12.073
TETL 48485
Reference:
Tetrahedron Letters
To appear in:
Received Date:
Revised Date:
Accepted Date:
25 November 2016
22 December 2016
23 December 2016
Please cite this article as: Samanta, S., Ravi, C., Joshi, A., Pappula, V., Adimurthy, S., Visible-light- induced aerobic
dioxygenation of styrenes under metal- and additive-free ambient conditions, Tetrahedron Letters (2016), doi: http://
dx.doi.org/10.1016/j.tetlet.2016.12.073
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2
Graphical Abstract
Visible-light- induced aerobic dioxygenation
of styrenes under metal- and additive-free
ambient conditions
Leave this area blank for abstract info.
Supravat Samanta, Chitrakar Ravi, Abhisek Joshi, Venkatanarayana Pappula and Subbarayappa Adimurthy*

1
Tetrahedron Letters
Visible-light- induced aerobic dioxygenation of styrenes under metal- and additive-
free ambient conditions
Supravat Samanta, Chitrakar Ravi, Abhisek Joshi, Venkatanarayana Pappula and Subbarayappa
Adimurthy*
Academy of Scientific & Innovative Research, CSIR–Central Salt & Marine Chemicals Research Institute, G.B. Marg, Bhavnagar-364 002. Gujarat (INDIA).
* E-mail: adimurthy@csmcri.org
ARTICLE INFO
ABSTRACT
Article history:
Received
Received in revised form
Accepted
Visible light promoted hydroperoxidation of styrenes using hydroxylamine and molecular
oxygen from air under metal-free and additive-free conditions at room temperature is described.
Hydroperoxides were further converted into corresponding hydroxy compounds and α-
oxygenated ketones in high yields under ambient conditions.
Available online
2009 Elsevier Ltd. All rights reserved.
Keywords:
Visible light
Hydroperoxidation
Styrenes
Metal-free
Additive-free
hydroperoxidation of styrenes using hydroxylamine and
molecular oxygen from air under metal-free conditions at room
temperature (Scheme 1). Further, the hydroperoxides were
transformed into corresponding hydroxy compounds and α-
oxygenated ketones in high yields using Me2S and
phenyliodoniumdiacetate respectively at ambient temperature.
These compounds generate variety of useful intermediates such
as vicinal 1,2-diols, β-hydroxy-N-alkoxyamines, α-haloketones,
α-azido ketones, β-ketoalkoxyamines and vinylphosphates upon
chemical modification.14,11b To the best of our knowledge, no
Oxygen is a highly atom-economical, environmentally benign
and abundant oxidant, which makes it ideal in many ways. The
construction of various types of oxygen-containing compounds
using molecular oxygen considered to be a vital and essential
subject in synthetic chemistry.1 As a result, significant progress
has been achieved by various groups during the past decade in
the area of molecular oxygen activation.2 Alkenes are the
simplest and most highly valuable starting materials and they can
be transformed into different oxygenated molecules such as 1, 2-
diols,3 α-hydroxyketones4 and 1, 2-dicarbonyl compounds.5
Recently, visible-light promoted chemical transformations have
received much attention in organic synthesis.6 Considering the
importance of photoredox catalysis, many groups have
demonstrated photo catalyzed organic transformations under
visible-light irradiation.7 Therefore, the exploitation of new
strategies and reagents to develop direct and greener
methodologies to avoid the use of expensive transition-metal
catalysts, toxic reagents, as well as explosive oxidants is highly
desirable.8
prior
reports available for the visible-light-promoted
dioxygenation of styrenes under metal-free and additive-free
conditions.
Transition metal-catalyzed oxygenation of hydrocarbons by the
activation of molecular oxygen has been well established.9
Among them, the dioxygenation of alkenes is an attractive
strategy due to the wide utility of oxygenated molecules in
synthetic chemistry.10 Therefore, substantial efforts have been
made by various groups for the dioxygenation of alkenes with
molecular oxygen to obtain β-keto-/β-hydroxy-N-alkoxyamines
systems.11 Recently, Punniyamurthy’s group developed an iron
catalyzed aerobic dioxygenation of styrenes for the synthesis of
β-hydroperoxy-N-alkoxyamines.12 In continuation of our interest
on functionalization olefins,13 in particular oxygenation of
Scheme 1. Aerobic dioxygenation of alkenes
We began our investigation with 4-methylstyrene 1a and N-
hydroxyphthalimide (NHPI) 2 as the model substrates and
subjected for oxidative dioxygenation at room temperature using
3W blue LED bulb in open atmosphere and the results are
summarized in Table 1. Initially, the reaction was performed
using 0.50 mmol of 1a, 0.50 mmol of 2 in CH3CN at room
styrenes,14 we report herein,
a
novel strategy on

2
temperature under 3W blue LED, after 18 hours 3a was isolated
in 82% yield (Table 1, entry 1). Increasing the amount of 2 to
0.55 mmol (1.1 equiv) and 0.60 mmol(1.2 equiv) led to increase
in the yield of 3a to 87% and 96 % respectively (Table 1, entries
2 and 3). By decreasing the reaction time from 18 h, the yield of
the product was dropped (Table 1, entries 4 and 5). When the
same reaction was performed under O2 atmosphere the desired
product 3a was obtained in 95% yield (Table 1, entries 6).
Further we screened the effect of other solvents on oxidative
dioxygenation of 1a, but no improvement was observed (Table 1,
entries 7-14). A control experiment showed that only a small
amount of product 3a was obtained in the absence of light (entry
15). When the same reaction was performed under sunlight for 9h
the desired product 3a was obtained in 55% yield (entry 16).
conjugated alkenes (3w-3z). More over to validate the
methodology, few example were performed at 5 mmol scale and
the results revealed that our strategy was effective at gram scale
preparation of products 3a, 3n, and 3r.
Table 2. Substrate scope for the visible-light-mediated of
dioxygenation of alkene with NHPI and HOBta.
Table 1. Optimization of the reaction conditions for 3aa
aReaction conditions otherwise stated: 1 0.50 mmol, 2 or 4 0.60 mmol, under
air and 3W blue LED, CH3CN (2.0 mL) at rt , for 18 h, isolated yields.
bReactions performed at 5.0 mmol of 1a, 6.0 mmol of 2 or 4.
Encouraged by the results obtained (products in Table 2), we
further sought to explore other hydroxylamines
5 (N-
hydroxysuccinimide (NHS) and methyl-N-hydroxy-N-
phenylcarbamate) for deoxygenation of styrenes. Reaction of
representative styrene derivatives under air with 25W CFL bulb
in open air at room temperature gave the desired dioxygenated
products 6a−d in 31−57% yields (Scheme 2).
aReaction conditions otherwise stated: 1a (0.50 mmol), 2 (0.60) mmol and
c
solvent (1.5 mL), at room
temperature. bIsolated yields. Reaction
performed under dark condition. d Reaction performed under sunlight for 9h.
Scheme 2. Oxidations with N-hydroxysuccinimide and
methyl-N-hydroxy-N-phenylcarbamatea
With the optimized conditions in hand, we explored the substrate
scope and limitations of
the visible-light-mediated
hydroperoxidation of various styrenes and the results are
compiled in Table 2. As evident from table 2, dioxygenation of a
variety of styrenes with NHPI were smoothly reacted and afford
the desired products in moderate to excellent yields. The reaction
of styrene 1b gave the corresponding compound 3b in 67% yield.
As expected, a variety of styrenes bearing both electron-donating
and/or electron withdrawing groups (R = Me, OMe, OAc, Ph,
tert-butyl, F, Cl and Br) at either (para/ortho/meta) position were
tolerated under the present reaction conditions and furnished the
expected products 3c–3k in 62-88% yields. The reaction of 1-
vinylnapthalene also proceeded well, giving the product 3l in
71% yield. It is noteworthy to mention that, α-methyl and phenyl
styrenes performed well and afforded the corresponding products
3m and 3n in moderate (60%) to excellent (98%) yields. Further,
trans-β-methyl styrene was also compatible under the present
reaction conditions, and the desired product 3o was obtained in
84% yield. Notably, cinnamyl alcohol was tolerable to these
conditions and delivered the product 3p in 51% yield. To explore
the present protocol, we performed the oxidation of the alkenes
1a, 1c, 1n and 1o having substituents on the aryl ring as well as
alkenes with N-hydroxybenzotriazole (HOBt) furnished the
corresponding peroxy products 3r–3v in 62-91%. Unfortunately,
the present protocol is not applicable for vinyl pyridine and non-
aReaction conditions otherwise stated: 0.50 mmol of 1a, 0.60 mmol of 2 or 4
in air under 25W CFL bulb, in 2.0 mL of CH3CN at r.t. for 48h, isolated
yields.
Scheme 3. Transformation of 3 to 7 hydroxy compoundsa
aReaction conditions unless stated: 3 (0.2 mmol), Me2S (1.2 mmol), CH2Cl2
b
(2.0 mL), 40˚C, 1.0h, isolated yields. Yields obtained from 1 (0.20 mmol), 2

3
Based on the above observations and the literature reports12, 16
a
or 4 (0.25 mmol) under air and 3W blue LED, CH3CN (1.0 mL), 18 h at room
temperature, then Me2S was added and reaction continued for another 1.0 h,
at 40˚C.
plausible reaction mechanism for dioxygenation of olefin is
outlined in Scheme 6. Initially R2NO• radical may be generated
from N-hydroxylamine (NHPI, HOBt) under visible light
conditions,16f which further react with olefin and generate a
carbon-centered radical intermediate A. The regioselectivity of
the reaction solely determines the stability of the benzylic radical
generation. In the presence of oxygen, A converts to peroxy
radical
The structural motifs of 7, are commonly found in many natural
products and are versatile intermediates in organic synthesis. Due
to the biological importance of these molecules, we studied the
transformation of 3 into alcohols 7 under unoptimized conditions.
The reaction of β-hydroperoxy-N-alkoxyamines 3a, 3b, 3d, 3n
and 3r with Me2S provided the corresponding hydroxy
compounds 7a–e in 91–96% yields at room temperature (Scheme
3).
Scheme 6. Plausible Mechanism
Finally, the reaction of β-hydroperoxy-N-alkoxyamines 3 were
extended with phenyliodoniumdiacetate (PIDA) to get α-
oxygenated ketones (Scheme 4). α-Oxygenated ketones are
extensively useful intermediates in both medicinal and biological
sciences.15 Considering the importance of these α-oxygenated
ketones, we further carried out the conversion of 3 to 8 under
unoptimized conditions. The reactions readily proceeded with
good to excellent yields. The reaction of 3a with PIDA
proceeded
Scheme 4. Transformation of 3 to α-oxygenated ketones (8)a
B, which may react with N-hydroxylamine to yield the desired
product.
In conclusion, we have demonstrated dioxygenation of styrenes
by employing hydroxylamine promoted by visible light under
aerobic conditions at room temperature without metal and
additives. The resulted dioxygenated products were further
transformed into synthetically useful compounds, such as
hydroxy compound and α-oxygenated ketones. Wide range of
substrate scope, scalability and high yields are the highlights of
present protocol.
aReaction conditions: 3 (0.3 mmol), PIDA (0.3 mmol), CH2Cl2 (2.0 mL), rt,
18h, isolated yields.
Acknowledgments
CSIR-CSMCRI Communication No. 139/2016. S.S, C. R &
A. J. are thankful to AcSIR for their Ph.D. enrollment and the
“Analytical Discipline and Centralized Instrumental Facilities”
for providing instrumentation facilities. S.S and A.J are also
thankful to CSIR, New Delhi for their fellowships. We thank
DST, Government of India (EMR/2016/000010), and CSIR-
CSMCRI (OLP-087) for financial support.
readily to yield 8a in 95% yield. Similarly the reaction of PIDA
with other substrates 3b, 3e, 3f, 3i, 3o and 3r, reacted smoothly
and furnished the corresponding α-oxygenated ketones 8b−g in
84−92% yields (Scheme 4).
To propose a probable mechanism for the present transformation,
some experiments were performed (Scheme-5). First, the reaction
of 1a was conducted in presence of radical scavenger, TEMPO
under optimized conditions, the TEMPO-adduct 9 was isolated in
21% yield instead of 3a. The same reaction with BHT, no desired
product formation was observed (Scheme 5). These controlled
experiments show that, the reaction may proceed through a
radical pathway. Further, the complete inhibition of the reaction
was observed under argon atmosphere indicates the molecular
oxygen is the source for insertion of oxygen in the product 3a.
Supplementary Material
Supplementary data (detailed experimental procedure and
spectroscopic data) associated with this article can be found,
in
the online version, at
Scheme 5. Mechanistic experiments

4
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5
Highlights
 Visible-light- induced aerobic
dioxygenation of styrenes.
 Synthesis of hydroperoxids and hydroxy
compounds
 Metal- and additive-free ambient conditions