Chemistry Reference
In-Depth Information
isolated yield (Scheme 7.23).
47
In 2010, the same research group further extended this
methodology to access potentially biologically active pyrroloquinolines with up to 85%
yield, with the application of [RhCl(CO)
2
]
2
as a precatalyst.
48
R
1
R
1
5mol%[Rh(cod)Cl]
2
11 mol% dppp
O
CO (1 atm), toluene
120
N
R
2
N
N
N
°
C, 1.5-2 h
R
2
R
1
=Me,Et,Ph,TMS
R
2
=alkyl,aryl
20-85% yield
Scheme 7.23
Rh-catalyzed PKR of alkynyl-carbodiimide.
In 2010, a pioneering work was developed by Chung and co-workers showing that
primary alcohols (such as cinnamyl alcohol) could be used as a CO surrogate for the
Rh-catalyzed intramolecular PK-type reaction (Scheme 7.24).
49
}
2
]
complex was found to effectively carry out this cascade reaction, in which alcohol se-
quentially conducted an oxidative dehydrogenation, decarbonylation and Pauson-Khand
reaction in one-pot. Various enyne substrates including
C
-,
O
- and
N
-tethered enynes were
examined. Up to 99% isolated yields were obtained.
The [
RhCl(CO)dppp
{
1
R
R
1
4 mol% [RhCl(CO)(dppp)]
2
130
°
C, 2 -18 h
OH
R
2
X
+
X
O
Conditions
A
or
B
R
2
53-99% yield
X = NTs, O, C(CO
2
Et)
2
R
1
=Me,Ph
R
2
=H,Me
A:
Cinnamyl alcohol (1.2 eq.), xylene
B:
Cinnamyl alcohol (4 eq.)
Scheme 7.24
Rh-catalyzed PKR of 1,6-enynes with cinnamyl alcohol as CO source.
In order to have a better picture for comparison between the rhodium catalysts, we have
summarized the turn-over activity of each catalyst as shown in Table 7.3.
7.3
Iridium-Catalyzed Pauson-Khand-Type Cyclizations
In 2000, Shibata and co-workers described the first Ir-catalyzed enantioselective intra- and
intermolecular Pauson-Khand-type reaction.
50
They used [Ir(cod)Cl]
2
and (
S
)-tol-BINAP as
the catalyst system for Pauson-Khand-type transformation and afforded the corresponding
cycloadducts in excellent ee, up to 98% (Scheme 7.25). Notably, the intermolecular product
yields and/or enantioselectivities were further improved under reduced partial CO pressure
(up to 93% ee at 0.2 CO atm).
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