3-BocNH-ABNO-catalyzed aerobic oxidation of alcohol at room temperature and atmospheric pressure

Article abstract of DOI:10.1016/j.tetlet.2019.150994

A transition-metal-free catalytic system has been developed for selective transformation of alcohol to aldehydes or ketones. The reactions were performed with 3-(tert-butoxycarbonylamino)-9-azabicyclo[3.3.1]nonane N-oxyl (3-BocNH-ABNO) as the catalyst, NaNO₂ as the co-catalyst, molecular oxygen as the terminal oxidant, and AcOH as the solvent under room temperature. This catalytic system exhibited broad functional group tolerance. A series of alcohol substrates, including primary and secondary benzylic alcohols, heteroaromatic analogues, primary and secondary aliphatic alcohols, could be converted into their corresponding aldehydes and ketones in good conversions and selectivities.

Full text of DOI:10.1016/j.tetlet.2019.150994

Evaluation Only. Created with Aspose.PDF. Copyright 2002-2021 Aspose Pty Ltd.
Journal Pre-Proof
3-BocNH-ABNO-catalyzed aerobic oxidation of alcohol at room temperature
and atmospheric pressure
Yajing Zhao, Yutong Li, Zhenlu Shen, Xinquan Hu, Baoxiang Hu, Liqun Jin,
Nan Sun, Meichao Li
PII:
S0040-4039(19)30749-X
https://doi.org/10.1016/j.tetlet.2019.150994
TETL 150994
DOI:
Reference:
Tetrahedron Letters
To appear in:
Received Date:
Revised Date:
Accepted Date:
10 June 2019
23 July 2019
27 July 2019
Please cite this article as: Zhao, Y., Li, Y., Shen, Z., Hu, X., Hu, B., Jin, L., Sun, N., Li, M., 3-BocNH-ABNO-
catalyzed aerobic oxidation of alcohol at room temperature and atmospheric pressure, Tetrahedron Letters (2019),
doi: https://doi.org/10.1016/j.tetlet.2019.150994
This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover
page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will
undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing
this version to give early visibility of the article. Please note that, during the production process, errors may be
discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
© 2019 Published by Elsevier Ltd.

Evaluation Only. Created with Aspose.PDF. Copyright 2002-2021 Aspose Pty Ltd.
JOURNAL PRE-PROOF
3-BocNH-ABNO-catalyzed aerobic oxidation of alcohol at room
temperature and atmospheric pressure
Yajing Zhao, Yutong Li, Zhenlu Shen*, Xinquan Hu, Baoxiang Hu, Liqun Jin, Nan Sun, Meichao
Li*
College of Chemical Engineering, Zhejiang University of Technology, Hangzhou 310014, China
E-mail address: zhenlushen@zjut.edu.cn; limc@zjut.edu.cn
Tel.: +86-571-88320305, fax: +86-571-88320305
Abstract:
A transition-metal-free catalytic system has been developed for selective transformation of
alcohol to aldehydes or ketones. The reactions were performed with 3-(tert-butoxycarbonylamino)-
9-azabicyclo[3.3.1]nonane N-oxyl (3-BocNH-ABNO) as the catalyst, NaNO2 as the co-catalyst,
molecular oxygen as the terminal oxidant, and AcOH as the solvent under room temperature. This
catalytic system exhibited broad functional group tolerance. A series of alcohol substrates, including
primary and secondary benzylic alcohols, heteroaromatic analogues, primary and secondary aliphatic
alcohols, could be converted into their corresponding aldehydes and ketones in good conversions and
selectivities.
Keywords: Oxidation; Molecular oxygen; Alcohols; Nitroxyl radicals

Evaluation Only. Created with Aspose.PDF. Copyright 2002-2021 Aspose Pty Ltd.
JOURNAL PRE-PROOF
Selective oxidation of alcohols to aldehydes or ketones is one of the most important organic chemical
reactions. This reaction is widely used in fine chemical industry, pharmaceutical synthesis, flavor and
fragrance industries [1]. To achieve this simple transformation, so far, a number of methods have
been developed. Traditionally, alcohol oxidation were achieved by using stoichiometric oxidants,
such as manganese oxides, chromium salts and the Dess-Martin reagent, which generated large
amounts of inorganic and organic wastes [2]. In recent years, molecular oxygen has attracted more
and more attention because of its abundant sources, low price and cleanliness [3]. From the viewpoint
of economy and environmental protection, it is undoubtedly the best alternative to use molecular
oxygen as the terminal oxidant in oxidation reaction. Based on these reasons, it needs great efforts to
develop aerobic oxidation methods.
In recent decades, use of 2,2,6,6-tetramethylpiperidine-N-oxyl (TEMPO) or its derivatives as
the catalyst in the aerobic oxidation of alcohols into carbonyl compounds has been widely reported
[4]. As is known to all, the nitroxyl radical of TEMPO is surrounded by four methyl groups, which
makes it possible to oxidize primary alcohols preferentially in the presence of secondary alcohols [5].
But this is precisely its disadvantage in the oxidation of sterically hindered primary and secondary
alcohols. Thus use of less hindered nitroxyl radicals as the catalyst offer a method to resolve this issue
(Scheme 1).
O
N
N
N
N
N
O
O
O
O
O
keto-ABNO
AZADO
1-Me-AZADO
TEMPO
ABNO
Scheme 1. Structures of different types of nitroxyl radicals.
For example, 2-azaadamantane N-oxyl (AZADO) was firstly synthesized by Dupeyre and Rassat
in 1975, but only in recent years it has been applied to alcohol oxidation [6]. Up to now, a lot of
catalytic systems for alcohol oxidation in which AZADO or its derivatives were chosen as the catalyst

Evaluation Only. Created with Aspose.PDF. Copyright 2002-2021 Aspose Pty Ltd.
JOURNAL PRE-PROOF
together with all sorts of terminal oxidants such as hypochlorite, chlorite, azodicarboxylates and
oxygen, have been established [7]. AZADO and its derivatives exhibited extraordinarily high
catalytic activity compared with TEMPO and its derivatives. However there are some drawbacks in
the procedure for the synthesis of AZADO and related nitroxyl derivatives, such as many synthetic
steps and poor yields. In contrast, the synthetic procedures of 9-azabicyclo[3,3,1]nonane N-oxyl
(ABNO) and its derivatives are relatively simple [8]. Recently, ABNO and keto-ABNO have been
widely employed as potent nitroxyl radicals for the oxidation of alcohols and other oxidation reactions
[9], and they exhibited highly active nature compared with TEMPO.
Previously, we reported a transition-metal-free catalytic oxidation system, TEMPO/tert-butyl
nitrite (TBN)/O2, for the aerobic oxidation of alcohols. In this oxidation system, TEMPO was
employed as the main catalyst, oxygen as the terminal oxidant, and TBN as the co-catalyst which
served as an equivalent of nitric oxide [10]. This aerobic oxidation system was expanded from our
previous oxidation systems, such as TEMPO/Br2/NaNO2/O2 [11], TEMPO/1,3-dibromo-5,5-
dimethylhydantoin/NaNO2/O2 [12], TEMPO/HBr/TBN/O2 [13], and extended to the DDQ/TBN/O2
and TEMPO/DDQ/TBN/O2 oxidation systems [14]. In 2013, Stahl et al successfully applied
ABNO/NaNO2/AcOH/O2, ABNO/NaNO2/HNO3/O2 and keto-ABNO/NaNO2/HNO3/O2 systems to
the oxidation of alcohols [15]. Very recently, we developed ABNO/TBN/KPF6/O2 system for the
oxidation of secondary alcohols in water [16].
To obtain a green, mild and efficient catalytic oxidation system, on the basis of literature and
previous research work of our group, herein we report a transition-metal-free catalytic system
consisting of 3-(tert-butoxycarbonylamino)-9-azabicyclo[3.3.1]nonane N-oxyl (3-BocNH-ABNO),
NaNO2 and AcOH for the selective aerobic oxidation of alcohols into their corresponding carbonyl
compounds (Scheme 2). Though 3-BocNH-ABNO has been reported several years ago [17], to our
knowledge, this work is the first example to apply 3-BocNH-ABNO to catalytic oxidation of alcohols
with molecular oxygen as the terminal oxidant.