1
88
Chemistry Letters Vol.36, No.1 (2007)
Oxone-mediated Methoxy Thiocyanation of 1,1-Disubstituted Olefins in Methanol
Ã
Guaili Wu, Wentao Wu, Rui Li, Yinglin Shen, and Longmin Wu
State Key Laboratory of Applied Organic Chemistry, Lanzhou University, Lanzhou 730000, P. R. China
(Received September 21, 2006; CL-061099; E-mail: wugl05@lzu.cn)
Reactions of 1,1-disubstituted olefins with oxone and
ammonium thiocyanate in methanol gave the corresponding
products and 1,2-dithiocyanated olefins 3 as minor outcomes
(Table 1).
1
-methoxy-2-thiocyano adducts in various yields.
The results in Table 1 indicate that the thiocyanation prefer-
red to occur regioselectively at the terminal carbon atom of C=C
double bond. Otherwise, the methoxy substituent in 2 shows
that methanol molecule participated the addition to olefins as a
As part of continuing efforts to explore a wider application
range of oxone in oxidative addition of thiocyanate to other
kinds of C=C double bond, further study was carried out to
extend the substrate scope for terminal alkenes, particularly for
3
nucleophile, leading to methoxylated products.
1
The reaction time in Table 1 clearly shows the substrates
displaying various reactivities toward the methoxy thiocyana-
tion. The speed of reactions appears to be influenced mainly
by electronic effects arising from substituents. An electron-do-
nating group linked at the para-position on the ring (1b and
1c) facilitated the reaction, whereas an electron-withdrawing
group slowed the reaction of 1f and 1g. It was so slow for 1g
as to have no thiocyanated product obtained. Another phenyl
group at the ꢀ-C (1e) led to highly slow the formation of end
product.
1,1-disubstituted olefins.
Several methods for the oxidative thiocyanation of alkenes
2
have been developed upon using an oxidant such as iodosoben-
2
a,2b,2c
2d
zene diacetate (IBDA),
CAN)2
I2/ICl, ceric ammonium nitrate
and (SCN)2, in which 1,2-dithiocyanates were
e,2f
2g
(
mainly yielded in most cases. It is noticed that the product struc-
tures and distributions are strongly oxidant- and solvent-depend-
ent, additional to the substrate structures and reaction conditions.
In general, the yields of thiocyanates were low and monothio-
cyanates hardly obtained as major outcomes.2 Hence, to learn
the oxidative reactivity of oxone in the addition of thiocyanate to
alkenes, to obtain a clear insight into the affects of oxidant on the
thiocyanation of alkenes, and to develop alternative approaches
accessible to the thiocyanation of alkenes are of considerable
academic interest. Otherwise, an oxidative vicinal addition of
alkoxy and nucleophile to the C=C double bond of olefins
Since solvent highly affected the addition of thiocyanate to a
C=C double bond, the effects of solvent on reaction proceeding
a,2b
Table 1. Methoxy thiocyanation of 1,1-disubstituted olefins in
methanol
1
2
a
b
Entry
R
R
t /h
Product yield/%
2
3
3
was found to occur in alcoholic solvents.
1a
Ph
CH
CH
CH
3
3
3
0.33
0.25
0.30
0.56
20
77
71
72
70
69
75
8.1
5.4
6.1
6.3
10
9.4
1b
1c
1d
1e
1f
4(CH
3
)Ph
)Ph
In the present work, we will disclose our results on the
formally simultaneous addition of methoxy and thiocyanate to
the terminal C=C double bond of 1,1-disubstituted olefins in
their reactions with oxone, as an oxidant, and ammonium thio-
4(OCH
3
c
Ph
Ph
CH
Ph
CH3
CH
3
CH
2
4(Br)Ph
4(NO )Ph
24
36
1
cyanate, as a thiocyanating reagent, in methanol (Scheme 1).
1g
2
3
New findings from the experiment have led us to a good under-
standing of the oxidant- and solvent-dependent addition of thio-
cyanate to olefins.
In a typical experiment, a solution of 118 mg of 1a (1.0
mmol) and 167 mg of ammonium thiocyanate (2.2 mmol) in
1
h
0.67
0.25
73
15
1
i
81
3.0
10 mL of anhydrous methanol was treated with 924 mg of oxone
(
1.5 mmol), allowed to stir at room temperature and monitored
by TLC. After completion of the reaction, the mixture was
filtered and dried under vacuum. The products were purified
by column chromatography on aluminum oxide neutral-gel
1
j
2
1
41
35
(
200–300 mesh, ethyl acetate/hexane) and provided as colorless
1
13
liquid. They were characterized by H and C NMR, IR,
FAB-MS or EIMS, and HR-ESI-MS. The reaction led to the
corresponding 1-methoxy-2-thiocyano added olefins 2 as major
1
k
R2
R2
R1
OMe
1.5
71
R2
SCN
1m
Oxone
SCN
+
R1
+
4
NH SCN
R1
SCN
MeOH, rt
1
2
3
a
b
The reaction time. Isolated yields of the products after column
chromatography. The dithiocyanated product was unstable.
c
Scheme 1.
Copyright Ó 2007 The Chemical Society of Japan
Wu, Guaili
