Chemistry Reference
In-Depth Information
Ph
Ph
5 mol% AuCl
3
, 15 mol% AgSbF
6
DCE, 50 °C
+
+
S
S
S
4.5:1
Scheme 24
Thiophene alkylation by styrene [
45
]
Ph
CH
2
OH
O
10 mol% Cp
2
ZrCl
2
CH
2
Cl
2
, rt, 18 h
+
S
S
17
Ph
71%
Scheme 25
Reaction of styrene epoxide with thiophene [
46
]
S
S
FG:
t
-Bu, CN, Ph, PO(OEt)
2
+
FG
FG
t
-Bu
t
-Bu
OH
81-97%
anti
syn
S
R
R
FG
HBF
4
. OEt
2
R
S
CH
2
Cl
2,
rt
R = Me, Et
FG: CO
2
Me
CO
2
Me
R
18
Scheme 26
Diastereoselective FC alkylation reactions of 2-methylthiophene with 1-(2
0
,2
0
,3
0
,
3
0
-tetramethylcyclopropyl)-alkan-1-ols [
47
]
50
C gave 2- and 3-alkylated thiophenes in the ratio 4.5:1 with an overall yield of
87% (Scheme
24
)[
45
].
Epoxide ring opening by thiophene was catalysed by 10 mol% of bis(cyclo-
pentadienyl)zirconium dichloride complex. The reaction was performed in aceto-
nitrile and, rather surprisingly, the 3-alkylated thiophene
17
was isolated in 71%
yield (Scheme
25
)[
46
].
2-Methylthiophene undergoes diastereoselective Friedel-Crafts-type alkylation
with 1-(2
0
,2
0
,3
0
,3
0
-tetramethylcyclopropyl)-alkan-1-ols under Brønsted acid cata-
lysis [
47
]. Tetramethylcyclopropyl-substituted carbocations formed under the reac-
tion conditions underwent a fast ring opening which led to the formation of allylic
cations, which by reaction with thiophene gave the products (Scheme
26
)[
47
].
In the case when R
CO
2
Me or CO
2
Et, the reaction pathway was different: here
the Friedel-Crafts reaction is faster than the formation of dehydrated cation, and it
¼
