Chemistry Reference
In-Depth Information
Recently, Shi
et al.
reported the synthesis of 4,5-disubstituted triazoles (Tria) as organic-
anionic ligands, and formed an air- and moisture-stable [Rh(cod)(Tria)]
2
complex as a
precatalyst for a Pauson-Khand reaction of 1,6-enyne (Scheme 7.17).
39
The best result was
obtained with ligand Tria-2 in up to 88% isolated yield.
N
N
Ph
N
N
N
N
5 mol% [Rh(cod)(Tria)]
2
Ph
6 mol% dppp
O
O
O
Ar
Me
Ar
CO (5 atm), xylene
130
Ph
Ar=Ph,
Tria-1
Ar=
p
-NO
2
C
6
H
4
,
Tria-2
Ph
°
C, 20 h
60-88% yield
Ar=Ph,
Tria-3
Ar=py,
Tria-4
Scheme 7.17
[Rh(Tria)dppp]-catalyzed PRK of 1,6-enyne.
In 2002, Mukai
40
and Brummond
41
independently reported Rh-catalyzed Pauson-
Khand-type cyclization involving allenyl moiety. By using the appropriate allenynes (allene-
alkyne substrates), the construction of seven-membered ring adducts was produced in
acceptable yields (Scheme 7.18).
40
R
R
SO
2
Ph
2.5 mol%
MeO
2
C
MeO
2
C
MeO
2
C
MeO
2
C
[RhCl(CO)dppp]
2
or [RhCl(CO)
2
]
2
O
Toluene, reflux, CO (1 atm)
SO
2
Ph
R = alkyl, aryl
45-84% yield
Scheme 7.18
The Rh-catalyzed PKR of allenynes.
In 2006, Mukai
et al.
further demonstrated a Rh-catalyzed intramolecular PK cycload-
dition of allenenes.
42
The intramolecular coupling of an allene-alkene substrate, which is
tethered by three or four atoms, afforded a bicyclic cyclopentenone with a 6-5 or 7-5 fused
ring system, respectively, along with the isomerization of carbon-carbon double bond. In
2010, the same research group further demonstrated a [
}
2
]-catalyzed in-
tramolecular PKR of bis(phenylsulfonylallene)s and afforded the desired bicyclic adducts
in up to
RhCl(CO)dppp
{
99% isolated yield (Scheme 7.19).
43
They suggested that the two phenylsulfonyl
groups on the allenyl functionalities were crucial to perform this carbonylative [2
+
2
+
1]
cycloaddition smoothly.
PhO
2
S
SO
2
Ph
5 mol% [RhCl(CO)dppp]
2
Toluene, 80 °C, CO (1 atm)
Z
Z
O
n
n
0.5-22 h
PhO
2
S
n
= 1, 2
SO
2
Ph
Z = O, NTs, C(CO Me) , TsN-NTs, CH
2
54->99% yield
2
2
Scheme 7.19
The Rh-catalyzed PKR of allene-alkene.
