Transcript 第八章 特殊试剂

第八章 特殊试剂
Chapter 8. Special reagents
主要内容
• 新试剂
• 含硼试剂：
• 含磷试剂：
• 含硅试剂：
• 含硒试剂：
• 含氮试剂：DCC, CDI
• 含硫试剂：
新试剂
• 含氮的双三溴化试剂：Ditribromide.
• 用于溴代反应等特殊官能团的转化。
1,1-(ethane-1,2-diyl)dipyridinium
bistribromide (EDPBT)
• Apart from bromination, it could also be used as a
catalyst for the acylation of alcohols, amines and
thiols, the silylation of hydroxyl groups and
desilylation of trimethylsilyl ethers, oxidation the
urazoles, bisurazoles to triazolinediones, and
sulfides to sulfoxides as well as the synthesis of 1(9-phenyl-9H-xanthen-9-yl)-propan-2-one,1,4dithiins,12 pifithrin,13 thiazolidene-2-imine and its
analogs. isothiocyanates from dithiocarbamates,
aryl–alkyl unsymmetrical thiourea, 2aminobenzimidazoles, An overview of the usage of
this new versatile reagent in organic synthesis was
presented below.
Preparation of EDPBT
• The reagent was prepared by refluxing 2 equivalents of pyridine
with 1 equivalent of 1, 2-dibromoethane. The intermediate 1,2dipyri-dinium dibromide-ethane (DPDBE) solid was treated with
KBr followed by oxidation of bromide to bromine, using an
aqueous solution of 1 equivalent of oxone20. The orange
precipitate was filtered and was recrystallized from acetonitrile
to obtain red crystals as EDPBT, which are stable for several
months at room temperature without loss of its activity
(Scheme 1). To regenerate the reagent without any significant
loss, the aqueous layer from the reaction was concentrated and
extracted with ethyl acetate to get rid of organic contaminants.
The KBr and oxone were added to the aqueous layer with
stirring. The precipitated orange solid was filtered as the
r e g e n e r a t e d
E D P B T .
EDPBT as a brominating agent
• Synthesis of α-haloketones:α-Haloketones
could be prepared in an excellent yield using
cyclohexanone or acetophenone and EDPBT
(0.5eq) in acetonitrile
• α-bromoarylacenones derivatives could be
prepared by the α-bromination reaction of
arylacenones with DPTBE as brominating agent
under solvent-free condition with a simple
procedure and excellent yield.
EDPBT as an oxidizing agent
• Synthesis of 1, 2, 4-triazolidine-3,5-diones: Triazoline
diones could be obtained by using EDPBT in CH2Cl2 as
an effective oxidizing agent to oxidate urazoles and
bisurazoles under a mild and heterogeneous condition at
room temperature with good to excellent yields.
Synthesis of the sulfoxides
• A wild range of aliphatic or aromatic sulfides
could be selectively oxidized using DPTBE in a
mixture of CH2Cl2/H2O2 as an oxidizing agent
under mild conditions in moderate to high yields.
EDPBT as a thiophilic reagent
• Synthesis of isothiocyanates from
dithiocarbamates：EDPBT has been used as a
thiophilic reagent to highly useful synthetic
intermediates (alkyl and aryl isothiocyanates)
directly from dithiocarbamates with high yield.
Fluorobenzyl isothiocyanates
• Fluorobenzyl isothiocyanates, which is an important
intermediate of 2,3-disubstituted-2-iminothiazoline-4ones, could be obtained from the fluoroanilines via
triethylamine salts of dithiocarbamic acids by using
EDPBT as a thiophilic reagent.
Synthesis of 2-aminobenzimidazoles
• Alkyl isothiocyanate reacts with ophenylenediamine (o-PD) to form corresponding
2-aminobenzimidazoles using EDPBT as a
thiophilic reagent
DPBT as a catalyst
• Synthesis of pentaerythritol esters: The pentaerythritol
reacted with acetic anhydride to give a diisopropylidine
derivative along with the isopropylidine diacetate in the
ratio (30/70). Changing the solvent from acetone to
acetonitrile resulted in the formation of pentaerythritol
tetra acetate as the sole product in nearly quantitative
yield
Catalyzing the acetylating process
of amines
• Acyl ammonias could be obtained by using Ac2O,
(i-PrCO)2O, (t-BuCO)2O and Bz2O as the
acetylating agents and catalyzed by EDPBT in
acetone with a good yield
Catalyzing the acetylating process
of alcohols
• Protic nucleophiles alcohols could be
transformed to their esters with a good yield in
acetone with the acetylating agents, such as
Ac2O, (i-PrCO)2O, (t-BuCO)2O and Bz2O, which
could be catalyzed by EDPBT.
Catalyzing the acetylating process
of thiols
• Aliphatic thiols could be transformed to their
thioesters in acetone with a good yield by using
Ac2O, (i-PrCO)2O, (t-BuCO)2O, Bz2O as the
acetylating agents and EDPBT as the catalyst
• EDPBT could be used as a
chemoselective and catalyzing both the
silylation of hydroxyl groups and the
desilylation of trimethylsilyl ethers an
effective organocatalyst for the silylation of
hydroxyl groups as well as the desilylation
of trimethylsilyl ethers under the mild
conditions with an excellent yields
EDPBT for other kind of reactions
• Synthesis of 1-(9-phenyl-9H-xanthen-9-yl)-propan-2-one
•
Tertiary alcohol reacted with HBr generated by EDPBT
in acetone to give a carbonation intermediate, which
underwent a nucleophilic attack by the enolized
acetones to afford the desired product.
Synthesis of 1,4-dithiins
• Acetophenone was treated with 1, 2-ethanedithiol and a
catalytic amount of EDPBT in acetonitrile to get the
corresponding 1,3-dithiolane, then further quantity of
EDPBT was added and the ring expanded to obtain the
1,4-dithiin in a good isolated yield
Synthesis of pifithrin
• Aminothiazole and triethylamine reacted with pmethylacetophenone by using EDPBT in
acetonitrile to form pifithrin as the inhibitor of
P53 in a 57% overall isolated yield
Synthesis of thiazolidene-2-imines
• 1, 3-Disubstituted thioureas reacted with an enolizable
ketone and EDPBT in the presence of triethylamine to
give thiazolidene-2-imine derivatives.14,15 This method
could also be used in generating bioconjugates, such as
anabolic thiazoloandrostane
Synthesis of aryl–alkyl
unsymmetrical thiourea
• The in situ generated aryl–alkyl unsymmetrical
thiourea obtained by the reaction of an aryl
isothiocyanate with an aliphatic secondary
amine treatment with EDPBT
Conclusions
• As one of the seldom reported bistribromide
reagent, 1-(ethane-1,2-diyl) dipyridinium
bistribromide (EDPBT) has received many
attentions for the possibilities of the usage in
organic chemistry for the merits of versatility,
recyclability, and regenerability. The summary of
the synthetic usage in this paper could provide
some information for further designing of new
similar reagent with more change of usage in
green chemistry.
含硼试剂
含硼试剂讨论主题
1 烯烃和硼烷的硼氢化反应
2 烯烃和烷基硼烷硼氢化反应
3 有机硼的反应反应
4 二烯的硼氢化反应
5 炔烃的硼氢化反应
6 羧酸的还原反应