O -benzenedisulfonimide as a recyclable homogeneous organocatalyst for an efficient and facile synthesis of 4-amidotetrahydropyran derivatives through prins-ritter reaction

Article abstract of DOI:10.1080/00397911.2014.909488

GRAPHICAL ABSTRACT A highly diastereoselective synthesis of 4-amidotetrahydropyran derivatives has been achieved using a catalytic amount of o-benzenedisulfonimide under mild conditions involving sequential allylation and Prins-Ritter amidation. The oxo-c

Full text of DOI:10.1080/00397911.2014.909488

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o-Benzenedisulfonimide as a Recyclable
Homogeneous Organocatalyst for an
Efficient and Facile Synthesis of 4-
Amidotetrahydropyran Derivatives
Through Prins–Ritter Reaction
B. V. Subba Reddy a & Supriya Ghanty a b
a Natural Product Chemistry , CSIR Indian Institute of Chemical
Technology , Hyderabad , India
b An Associate Institution of University of Hyderabad , Hyderabad ,
India
Published online: 02 Jul 2014.
To cite this article: B. V. Subba Reddy & Supriya Ghanty (2014) o-Benzenedisulfonimide
as a Recyclable Homogeneous Organocatalyst for an Efficient and Facile Synthesis of 4-
Amidotetrahydropyran Derivatives Through Prins–Ritter Reaction, Synthetic Communications: An
International Journal for Rapid Communication of Synthetic Organic Chemistry, 44:17, 2545-2554,
DOI: 10.1080/00397911.2014.909488
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Synthetic Communications1, 44: 2545–2554, 2014
Copyright # CSIR Indian Institute of Chemical Technology
ISSN: 0039-7911 print=1532-2432 online
DOI: 10.1080/00397911.2014.909488
o-BENZENEDISULFONIMIDE AS A RECYCLABLE
HOMOGENEOUS ORGANOCATALYST FOR AN
EFFICIENT AND FACILE SYNTHESIS OF
4-AMIDOTETRAHYDROPYRAN DERIVATIVES
THROUGH PRINS–RITTER REACTION
B. V. Subba Reddy1 and Supriya Ghanty1,2
1Natural Product Chemistry, CSIR Indian Institute of Chemical Technology,
Hyderabad, India
2An Associate Institution of University of Hyderabad, Hyderabad, India
GRAPHICAL ABSTRACT
Abstract A highly diastereoselective synthesis of 4-amidotetrahydropyran derivatives has
been achieved using a catalytic amount of o-benzenedisulfonimide under mild conditions
involving sequential allylation and Prins–Ritter amidation. The oxo-carbenium ion formed
in Prins cyclization could be successfully trapped with nitriles through Ritter amidation.
The catalyst is highly efficient in promoting both allylation and Prins cyclization with a
net addition of nitrile. The catalyst can be easily recovered and reused in subsequent
reactions.
Keywords 4-Amidotetrahydropyrans; Brønsted acid; Hosomi–Sakurai allylation;
Prins–Ritter amidation; recyclable catalyst; spiro-tetrahydropyrans
Received December 5, 2013.
Address correspondence to B. V. Subba Reddy, Natural Product Chemistry, CSIR Indian Institute
of Chemical Technology, Hyderabad 500 007, India. E-mail: basireddy@iict.res.in
2545

2546
B. V. S. REDDY AND S. GHANTY
INTRODUCTION
In recent years, o-benzenedisulfonimide (1, 1,3,2-benzodithiazole-1,1,3,
3-tetraoxide; Fig. 1) has received great attention because of its versatility in organic
synthesis. It has been used for various organic transformations such as
etherification=acetalization,[1] esterification,[2] Hosomi–Sakurai reaction,[3] Ritter
reaction,[4] Nazarov electrocyclization,[5] disproportionations of dialkyl diarylmethyl
ethers,[6] and Strecker reaction.[7] It can be recovered and reused in subsequent
reactions with economic and ecological advantages.
4-Aminotetrahydropyran ring is a core structure in several natural products[8]
such as ambruticin VS3 and dysiherbaine (Fig. 2). Compound A is a heat-generating
photosensitive material used in photographic films. Compound B, a nonmacrocyclic
supramolecule, showed appreciable binding with alkali metals (Liþ, Naþ, and Kþ)
with association constants (Ka) greater than 107–108, and compound C is a
melanocortin receptor agonist.[9]
In literature, a few one-pot approaches have been reported for the synthesis of
4-amidotetrahydropyrans. Typically, these methods combine three reactions such as
Figure 1. o-Benzenedisulfonimide (OBS) (1).
Figure 2. Representative examples of 4-aminotetrahydropyrans.

ORGANOCATALYST FOR THE PRINS–RITTER REACTION
2547
(i) Sakurai–Hosomi, (ii) Prins cyclization, and (iii) Ritter amidation in a one-pot
operation. However, most of these methods require activators such as acetyl chloride
and stoichiometric amount of catalysts. Hence, there is still scope to develop cata-
lytic methods with low catalytic loading and high efficiency for the synthesis of
4-amidotetrahydropyran derivatives.[10] In this article, we report a new application
of o-benzenedisulfonimide (1) to perform the Prins–Ritter amidation. The catalyst
is a nontoxic, nonvolatile, and noncorrosive homogeneous Brønsted acid.
RESULTS AND DISCUSSION
Following our interest in Prins cyclization,[11] we herein report an efficient
and rapid approach for the synthesis of symmetrical 2,6-disubstituted 4-amidotetra-
hydropyrans through a sequential Sakurai–Hosomi–Prins=Ritter reaction. The
Hosomi–Sakurai allylation of both aromatic and aliphatic aldehydes proceeds rap-
idly under the influence of the catalyst (1). Thus in situ–formed homoallylic alcohol
underwent a smooth Prins cyclization with another equiv. of aldehyde in the pres-
ence of nitrile to afford the corresponding 4-amidotetrahydropyran. For instance,
treatment of 2.1 equiv. of p-chlorobenzaldehyde with 1 equiv. of allyltrimethylsilane
in acetonitrile in the presence of 10 mol% catalyst (1) at room temperature gave the
corresponding 4-acetamido-2,6-diphenyl-tetrahydropyran 3a in 85% yield with cis-
selectivity. The reaction was completed within 1 h with excellent diastereoselectivity
(Table 1, Scheme 1).
Unlike classical Prins cyclization, no formation of undesired 4-hydroxytetrahy-
dropyrans was observed when a catalytic amount of catalyst (1) was employed.
These results encouraged us to extend this protocol for various aldehydes and
nitriles. Interestingly, aromatic aldehydes such as p-chlorobenzaldehyde and p-
bromobenzaldehyde underwent a smooth reaction with allyltrimethylsilane in
acetonitrile to give the corresponding 4-acetamido-2,6-diaryl-tetrahydropyrans in
good yields (entries a and b, Table 1). This method is effective even for sterically hin-
dered substrate, for example, 2-naphthaldehyde (entry c, Table 1). Similarly, benzal-
dehyde also reacted well with allyltrimethylsilane in benzyl cyanide to yield the
corresponding 2,6-diaryl-4-phenylacetamido-tetrahydropyrans (entry d, Table 1).
Next, we studied the reactivity of aromatic and aliphatic aldehydes in benzonitrile.
Interestingly, p-chlorobenzaldehyde and n-butanal participated well in the Hosomi–
Sakurai–Prins=Ritter amidation in benzonitrile to yield the respective 2,6-
disubstituted-4-benzamidotetrahydropyrans (entries e and f, Table 1). Thus, it is very
useful for the preparation of a diverse range of 2,6-diaryl- or 2,6-dialkyl-4-amidote-
trahydropyrans. The structures of the products were established by NMR, infrared
(IR), and mass spectroscopy. It is noteworthy to mention that the reaction was not
successful in the absence of acid catalyst (1) even after an extended reaction time
(12 h). The products were obtained in good yields with cis-selectivity as confirmed
from the NMR spectrum of the crude product. Only a single diastereoisomer was
formed in each reaction, the structure of which was confirmed by coupling constants
(J values) and nuclear Overhauser effect (nOe) experiments.[8] The scope of the cata-
lyst 1 is illustrated with respect to various aldehydes and the results are presented in
Table 1. As shown in Table 1, this method works well with both electron-donating as
well as electron-withdrawing aldehydes.

2548
B. V. S. REDDY AND S. GHANTY
Table 1. o-Benzenedisulfonimide catalyzed Prins=Ritter reaction
Entry
Aldehyde
Nitriles
CH3CN
Product (3)a
Time (h) Yield (%)b
a
1.0
1.0
85
86
b
CH3CN
c
CH3CN
1.5
1.0
82
80
d
e
f
1.5
1.5
91
80
aAll products were characterized by 1H NMR, IR and mass spectrometry.
bYield refers to pure products after chromatography.
Scheme 1. Sequential allylation and Prins–Ritter amidation.

ORGANOCATALYST FOR THE PRINS–RITTER REACTION
2549
The simplicity of this procedure encouraged us to further extend it to the
preparation of unsymmetrical 4-amidotetrahydropyran derivatives by means of
Prins–Ritter reaction (entries 4a–g, Table 2). In a typical experiment, 1.2 eq of
Table 2. o-Benzenedisulfonimide–catalyzed Prins=Ritter reaction
Homoallyl
alcohol
Time Yield
(%)b
Entry Aldehyde=Ketone
Nitriles
CH3CN
Product (4)a
(h)
a
1.0
87
b
c
CH3CN
1.0
1.2
80
80
d
1.2
1.0
82
90
e
CH3CN
f
1.2
1.0
83
80
g
CH3CN
aAll products were characterized by 1H NMR, IR and mass spectrometry.
bYield refers to pure products after chromatography.

2550
B. V. S. REDDY AND S. GHANTY
Scheme 2. Preparation of 2-phenyl-4-amidotetrahydropyran 4a.
Scheme 3. Spiro-4-amidotetrahydropyran 4g.
p-chlorobenzaldehyde was treated with 1.0 eq of 3-buten-1-ol in the presence of
10 mol% of catalyst 1 in acetonitrile. Interestingly, the reaction was completed within
1 h at room temperature and the corresponding 2-phenyl-4-acetamidotetrahydro-
pyran 4a was obtained in 87% yield with cis-selectivity (Table 2, Scheme 2).
Subsequently, we found that this method works not only with aldehydes but
also with ketones. For instance, N-methylisatin (1-methylindoline-2,3-dione) reacted
smoothly with 3-buten-1-ol in the presence of catalyst 1 (10 mol%) in acetonitrile to
furnish the corresponding spiro-tetrahydropyranyl amide[12] 4g in 80% yield
(Scheme 3, entry g; Table 2).
Next, we tested the efficiency of o-benzenedisulfonimide with known acid cat-
alysts for the condensation of homoallylic alcohol with N-methylisatin in acetonitrile
at 25 ꢀC, and the results are presented in Table 3.
Table 3. Screening of various acid catalysts in the formation of 4g
Entry
Catalysts (10 mol%)
Reaction time
Yield (%)a
a
b
c
HCOOH
BF3.OEt2
12 h
10 h
12 h
12 h
10 h
10 h
10 h
1.0 h
Trace
50
40
Phosphomolybdic acid
TFA
d
e
45
60
4-MeC6H4SO3H
MeSO3H
NH2SO3H
f
63
40
g
h
o-Benzenedisulfonimide
80
aYield refers to pure product after chomatography.

ORGANOCATALYST FOR THE PRINS–RITTER REACTION
2551
As seen from Table 3, the product 4g was obtained in 80% yield in a shorter
reaction time (1 h) with o-benzenedisulfonimide compared to other acid catalysts.
Thus, o-benzenedisulfonimide was found to be a superior catalyst in promoting
Prins–Ritter amidation. It is the first example of Prins–Ritter amidation of N-
methylisatin, which may find a useful application in medicinal chemistry to generate
spiro-cyclic oxindole scaffolds.
The catalyst 1 is a strong acid[7] and soluble in both water and organic solvents.
One of the most remarkable aspects in the use of 1 is its ease of recovery in good
yields from the reaction mixture owing to its complete solubility in water and its
reuse in further reactions without significant loss of catalytic activity. The use of
recyclable Brønsted acid (1) in this transformation makes this method an economi-
cally viable process for the synthesis of 4-amidotetrahydropyran derivatives. The
recovered catalyst 1 was recycled in several consecutive runs and the results are pre-
sented in Table 4. The yields of 4a and the recovery of 1 are always excellent
throughout the course of different runs.
The cis-selectivity of the Prins–Ritter amidation reaction can be explained by
the formation of oxo-carbenium ion in the presence of an acid catalyst. Attack of
the alkene to oxo-carbenium ion through a chair-like transition state generates a
tetrahydropyranyl cation. In the ring closure step, the C2 substituent occupies favor-
ably in equatorial position to produce (E)-oxo-carbenium ion over the (Z)-oxo-
carbenium ion. Therefore, the stereochemistry of the C2 substituent is transferred
to the newly formed carbon–carbon bond. The stereochemistry at C4 is controlled
by the extensive delocalization of the tetrahydropyranyl cation. The optimal
geometry for this delocalization places hydrogen at C4 in a pseudoaxial position,
so the nucleophilic attack occurs from the equatorial side to deliver the cis-tetrahy-
dropyran skeleton.[13]
In summary, a direct one-pot method has been developed for the synthesis
of 4-amidotetrahydropyran derivatives by means of Prins cyclisation using
a recyclable Brønsted acid catalyst (1). The synthetic usefulness of o-benzenedi-
sulfonimide (1) as an organocatalyst in Prins–Ritter reaction has been demon-
strated. This strong bench-stable Brønsted acid has been shown to catalyze the
three-component Prins–Ritter amidation under mild conditions. This method
provides easy access to the synthesis of a wide range of symmetrical, unsym-
metrical, and spiro-cyclic 4-amidotetrahydropyran derivatives with excellent
yields (Scheme 4).
Table 4. Reusability of the catalyst (1) in the preparation of 4aa
Entry
Yielda (%) (4a)b
Recovery (%) (1)c
1
2
3
4
87
82
80
78
85 (18.6 mg)
81 (15.06 mg)
78 (11.75 mg)
75 (8.23 mg)
aAll the reaction were performed in 1 h.
bYield refers to the pure product.
cThe reaction was performed in 1 mmol scale using 0.1 mmol of the catalyst (1).

2552
B. V. S. REDDY AND S. GHANTY
Scheme 4. Plausible reaction pathway.
EXPERIMENTAL
Representative Procedure for the Synthesis of
4-Amidotetrahydropyran Derivatives
A solution of allyltrimethylsilane (0.5 mmol) was added to a mixture of alde-
hyde (1.05 mmol) and o-benzenedisulfonimide (1) (10 mmol%) in nitrile (4 mL).
The resulting mixture was stirred at room temperature for the specified time. After
completion, as indicated by TLC, the reaction mixture was poured into
dichloromethane=water (20 mL, 1:1). The aqueous layer was separated and extracted
with dichloromethane (3 ꢁ 15 mL). The combined organic layers were washed with
water (3 ꢁ 4 mL), dried over anhydrous Na2SO4, and concentrated in vacuo. The
resulting crude mass was then subjected to flash column chromatography using a
7:3 mixture of n-hexane and ethyl acetate as eluent to afford the pure 4-amidotetra-
hydropyran. The products thus obtained were characterized by infrared (IR), NMR,
and mass spectroscopy. The spectroscopic data of products 3a, 3c, and 3f (Table 1)
and 4a (Table 2) are known in the literature.[10]
The aqueous layer and aqueous washings were collected and evaporated under
reduced pressure. The residue was passed through a column of Dowex AG 50W-X8
ion-exchange resin (acidic in nature, 100–200 mesh, 160 mg resin=100 mg product)
with water as eluent. After removal of the water under reduced pressure, virtually
the pure catalyst 1 was recovered as a white solid; mp 190–192 ꢀC (toluene) (lit.[14]
192–194 ꢀC). The recovered catalyst 1 was employed in further catalytic cycles under
the conditions described previously.
FUNDING
S. G. thanks the Council of Scientific and Industrial Research, New Delhi, for
the award of a fellowship.
SUPPLEMENTAL MATERIAL
1
Full experimental details and H and 13C NMR spectra are available online.
Supplemental data for this article can be accessed on the publisher’s website.

ORGANOCATALYST FOR THE PRINS–RITTER REACTION
2553
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