Tetrahedron Letters
Synthesis of 2-tetralone derivatives by Bi(OTf)3-catalyzed
intramolecular hydroarylation/isomerization of propargyl alcohols
Jihee Yun a, Jungmin Park a, Jaehyun Kim a, Kooyeon Lee a,b,
⇑
a Department of Bio-Health Technology, Kangwon National University, Chuncheon 200-701, Republic of Korea
b Institute of Bioscience and Biotechnology, Kangwon National University, Chuncheon 200-701, Republic of Korea
a r t i c l e i n f o
a b s t r a c t
Article history:
Compared to 1-tetralones, 2-tetralones are expensive, less stable, and difficult to synthesize. A concise
Bi-catalyzed method was developed for the synthesis of 2-tetralones from 5-phenylpent-1-yn-3-ol deriv-
atives. Diverse 2-tetralones were obtained in moderate to good yields under mild conditions.
Ó 2015 Elsevier Ltd. All rights reserved.
Received 27 August 2014
Revised 17 December 2014
Accepted 26 December 2014
Available online xxxx
Keywords:
Bi catalyst
2-Tetralone
Propargyl alcohol
Intramolecular hydroarylation
Isomerization
2-Teralones are important scaffolds in biologically active natural
products, pharmaceuticals, and other useful materials;1 however,
they are difficult to synthesize.2 Existing synthetic methods for
2-tetrlones include the 1,2-transposition of the carbonyl group of
1-tetralones,3 reduction of substituted 2-methoxynaphthalenes,4
CH3
Bi(OTf)3 (10 mol%)
DCE, 80 o
Scheme 1. Synthesis of 2-tetralone derivatives.
OH
O
R1
R1
C
Rh(II)-catalyzed cyclization of
a
-diazoketones,5 SnCl4-mediated
cyclization of propargyl alcohols,6 Pummerer rearrangement-
mediated cyclization of aryl b-ketosulfoxides,7 and the Friedel–
Crafts reaction of aromatic acyl chlorides with olefins.8 However,
these reactions suffer from the use of expensive (rhodium) and
harmful (diazoketone and b-ketosulfoxide) reagents, long reaction
sequences, and low-to-moderate yields. Therefore, a more efficient
method needs to be developed for the synthesis of 2-tetralone con-
sidering their importance. Recently, In(III)-promoted cyclization/
isomerization reaction of propargyl alcohols has been reported.9
Although this procedure provides an efficient one-step synthetic
route for the synthesis of 2-tetralone, the substrate scope of 2-tetral-
ones was narrow. Recently, we reported the intramolecular hydro-
arylation reactions of aryl alkynes using a Brønsted acid or Au
catalyst.10,11 In our previous studies, we found that Fe or Bi salts
element and has been widely used in synthetic chemistry over the
last few years.13 In particular, Bi(OTf)3 is a well-known efficient cat-
alyst for dual activation via r,p
-chelation.14 In this Letter, we report
the Bi(OTf)3-catalyzed one-step synthesis of 2-tetralones from aryl
propargyl alcohols. We have used 5-phenylpent-1-yn-3-ol 1a as a
useful functionality in organic synthesis; as a model reaction, the
reaction of 1a with a catalytic amount of Bi(OTf)3 afforded 2-
tetralone in good yields (Scheme 1).
First, various types of propargyl alcohols 1 were prepared in good
to excellent yields by classic methods.15 The reduction of commer-
cially available cinnamic acids with LAH in THF afforded the corre-
sponding saturated alcohols. Next, the reaction of primary alcohols
with PCC in CH2Cl2 afforded the corresponding aldehydes in good
yields. Finally, the Grignard addition of ethynylmagnesium bromide
to the aldehydes afforded the corresponding 5-phenylpent-1-yn-3-
ol derivatives 1.
are efficient catalysts for the
p
-activation of C–C triple bonds.12
Therefore, we envisioned that Fe or Bi salts are sufficient catalysts
for the synthesis of 2-tetralones by intramolecular hydroarylation/
isomerization reactions. Bi is known as an environmentally benign
To optimize the catalyst for the intramolecular hydroarylation/
isomerization of 5-phenylpent-1-yn-3-ol derivatives 1, diverse
Lewis and Brønsted acids were screened using 1a as the model sub-
strate (Table 1). Various Fe salts were investigated as catalysts for
the synthesis of 1-methyl-2-tetralone 2a in DCE. The reaction of
⇑
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0040-4039/Ó 2015 Elsevier Ltd. All rights reserved.