Bi(OTf)3-catalyzed Baeyer-Villiger oxidation of carbonyl compounds with m-CPBA

Article abstract of DOI:10.1081/SCC-120022478

An efficient method has been developed for the Baeyer-Villiger oxidation of a variety of carbonyl compounds with m-CPBA to afford the corresponding esters/lactones using bismuth triflate as catalyst. The catalyst is reused for Baeyer-Villiger oxidation without significant loss of catalytic activity for three cycles.

Full text of DOI:10.1081/SCC-120022478

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Bi(OTf)3-Catalyzed Baeyer–Villiger Oxidation of
Carbonyl Compounds with m -CPBA
M. Mujahid Alam a , Ravi Varala a & Srinivas R. Adapa a
a ICICI Knowledge Park , The Product Discovery Centre , Indian Institute of Chemical
Technology , Hyderabad, India
Published online: 21 Aug 2006.
To cite this article: M. Mujahid Alam , Ravi Varala & Srinivas R. Adapa (2003) Bi(OTf)3-Catalyzed Baeyer–Villiger Oxidation
of Carbonyl Compounds with m -CPBA, Synthetic Communications: An International Journal for Rapid Communication of
Synthetic Organic Chemistry, 33:17, 3035-3040, DOI: 10.1081/SCC-120022478
To link to this article: http://dx.doi.org/10.1081/SCC-120022478
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SYNTHETIC COMMUNICATIONSÕ
Vol. 33, No. 17, pp. 3035–3040, 2003
Bi(OTf)3-Catalyzed Baeyer–Villiger Oxidation
of Carbonyl Compounds with m-CPBA
*
M. Mujahid Alam, Ravi Varala, and Srinivas R. Adapa
ICICI Knowledge Park, The Product Discovery Centre,
Indian Institute of Chemical Technology,
Hyderabad, India
ABSTRACT
An efficient methodhas been edvelopedfor the Baeyer–Villiger
oxidation of a variety of carbonyl compounds with m-CPBA to
affordthe corresponding esters/lactones using bismuth triflate as
catalyst. The catalyst is reusedfor Baeyer–Villiger oxidation without
significant loss of catalytic activity for three cycles.
Key Words: Baeyer–Villiger oxidation; m-CPBA; Bismuth triflate
(Bi(OTf)3).
*Correspondence: Srinivas R. Adapa, ICICI Knowledge Park, The Product
Discovery Centre, Indian Institute of Chemical Technology, Hyderabad,
500 007 India; Fax: 040-7160921; E-mail: asrinivas_rao@iict.ap.nic.in.
3035
DOI: 10.1081/SCC-120022478
Copyright & 2003 by Marcel Dekker, Inc.
0039-7911 (Print); 1532-2432 (Online)
www.dekker.com

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3036
Alam, Varala, and Adapa
The Baeyer-Villager oxidation, first reported more than 100 years
ago,[1] has evolvedinto a versatile reaction widely used
[2]
to convert
ketones that are readily available building blocks into more complex
and valuable esters and lactones using peracids or hydrogen peroxide.[3]
Among these m-CPBA is the most commonly usedoxidant because
it provides a simple and efficient alternative to the existing procedures
for this reaction.[4] To enhance the reactivity, the combineduse of the
m-CPBA with appropriate catalysts such as sulfonic acids,[5] Nafion-H,[6]
[9]
CF3COOH,[7] hydrotalicite,[8] andSnCl
,
has been widely used.
4
Recently, scandium triflate[10] has also shown to be a very efficient
catalyst for this reaction. Unfortunately, scandium triflate is very expen-
sive andrecovery of spent scanidum triflate is very idfficult from
the reaction mixture. Thus, the use of scandium triflate in large-scale
synthesis is very limited. Thus, there is a greater need for developing
cheaper, andefficient catalytic methoodlogies for Baeyer–Villiger
oxidation of carbonyl compounds.
In this direction, bismuth triflate is the center of focus to organic
chemists.[11] It is of great interest to evaluate the utility of bismuth triflate
as an efficient catalyst for Baeyer–Villiger oxidation of carbonyl
compounds using m-CPBA (Sch. 1). We are particularly interestedin
bismuth triflate, because it is inexpensive,[12] andcan be easily prepared
in laboratory from commercially available bismuth (III) oxide and triflic
acid.[13] The results from our study are presented herein.
Initially, we have studied the Baeyer–Villiger oxidation of 4-t-butyl
cyclohexanone (Table 1, Entry 4) as a model substrate with 2 equiv of
m-CPBA (80% activity) using a catalytic amount of bismuth triflate. The
most satisfactory result was obtainedfor the reaction using 5 mol% of
bismuth triflate which gave the desired lactone quantitatively in a much
short reaction time. In fact, almost 5–7 times acceleration has been
achievedhere when comparedwith the model substrate using m-CPBA
alone. It was foundthat dichloro methane was the best solvent for this
reaction. When acetonitrile andethyl acetate were usedas solvents better
yields were obtained while THF and acetone gave very poor yields for the
model substrate. Next, reusability of the spent catalyst for the model
Scheme 1.

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Baeyer–Villiger Oxidation
3037
a
.
Table 1. (Bi(Otf)3-catalyzedBaeyer–Villiger oxidation of carbonyl compound
Entry
1
Substrate
Time
Products
Yield (%)
90
O
O
O
20 min
O
O
O
2
3
30 min
30 min
100
95c
O
O
O
O
O
+
O
O
4
5
20 min
45 min
99d
O
90e
O
o
O
6
7
1 h
80(56:24)
72
O
O
+
O
O
o
O
O
O
2.5 h
COCH3
OMe
COCH
3
O
8
4 h
85
OMe
90f
70
CHO
OCHO
9
3 h
O
10
6.5 h
O
O
(continued )

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3038
Alam, Varala, and Adapa
Table 1. Continued.
Entry
11
Substrate
Time
22 h
Products
Yield (%)
65
O
O
O
O
12
8 h
55
O
O
aUnless otherwise noted, all reactions were performed using 2 equiv. of m-CPBA
in the presence of Bi(OTf)3 (5 mol%) in DCM at rt.
bIsolatedyield.
cCal 1:1.
dIst use, 99%; 2nduse, 96%; 3rduse 90%.
eA regioisomer is 8% of products.
fUnavoidable hydrolysis of 2-naphthyl formate was observed during column
chromatographic purification.
substrate reaction was examined. The catalyst was simply recovered
almost quantitatively by simple filtration of the crude reaction mixture,
and air-dried to yield. This recovered catalyst was reused up to three
cycles for 4-tert butyl cyclohexanone for effecting Baeyer–Villiger oxida-
tion using m-CPBA (Table 1, Entry 4d). These reactions afforded corre-
sponding oxidation product in good yields comparable to those obtained
with fresh catalyst and no significant decrease in yield of the product was
observed. These results demonstrate that bismuth triflate is a robust
catalyst for effecting Baeyer–Villiger reaction.
Encouragedby these results, we have carriedout bismuth triflate
catalyzedBaeyer–Villiger oxidation of a variety of ketones to better
understand both the scope and the generality of the reaction. Only a
freshly preparedbismuth triflate catalyst was usedin these studies. The
results from our study are summarized in Table 1, and in all cases good to
excellent yields were obtained. As shown in Table 1, aliphatic cyclic
ketones took much shorter reaction times than those of acyclic or
aromatic ketones. In general, goodstereo selectivity was observedwith
the product arising from preferential migration of the more substituted
carbon atom. 3-Methyl cyclohexanone gave a mixture of 5-methylcapro-
lactone and3-methylcaprolactone (cal.1:1, Entry 3). Interestingly,
cyclohexenone (Table 1, Entry 6) gave corresponding epoxide as major
product. For 2-allylcyclohexanone (Table 1, Entry 7), only a single

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Baeyer–Villiger Oxidation
3039
product was formed even though such Baeyer–Villiger oxidation could
lead to two different products for this reaction. Similar chemoselectivity
has also been observedwhen benzyl phenyl ketone was usedas substrate
wherein selective migration of the benzyl group afforded benzyl benzoate.
(Table 1, Entry 12). These results clearly indicate bismuth triflate could
impart chemoselectivity in high degree for these substrates.
In conclusion, we have shown that Baeyer–Villiger reactions
on a variety of ketone substrates can be efficiently performedat room
temperature using m-CPBA as an oxidant and bismuth triflate under mild
reaction conditions. Additionally, the catalyst could be recovered easily
from the reaction mixture andreusedwithout significant loss of catalytic
activity. Further studies are currently underway to perform such
reactions under heterogeneous conditions.
Typical procedure of the Baeyer–Villiger oxidation of ketones. To a
mixture of an appropriate ketone (2 mmol) andBi(OTf) (5 mol%) in
3
10 mL of anhydrous dichloromethane at 0ꢀC was added commercial
grade m-CPBA (80% activity, 863 mg, 4 mmol) andthe reaction mixture
was stirredat room temperature. After the completion of the reaction,
the catalyst was separatedby simple filtration andunreacted m-CPBA
was decomposed by addition of an aq. Na2S2O3 solution. The product
was extractedusing ethylacetate, andall the organic extracts were
combined, dried over anhydrous Na2SO4, concentratedto yieldcrude
product. Purification by silica gel column chromatography gave the
corresponding ester or lactone in good yields. All the products are
characterizedby comparing their physical data, 1H-NMR, Mass, IR of
authentic samples.
ACKNOWLEDGMENT
M. M. Alam andV. R thank Dr. B. M. Choudary, Headof the
Division, Dr. K. V. Raghavan, DIICT for their constant support
throughout the work.
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Receivedin the UK November 19, 2002