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Scheme 4.49 Ir(I)-catalyzed cyclocarbonylation reaction by Shibata.
O
•
317
Ph
H
O
•
Ph
5 mol % IrCl(CO)(PPh 3) 2
xylene, 120 o C
CO(0.2 atm)
5 mol % IrCl(CO)(PPh 3) 2
xylene, 120 o C
CO(0.2 atm), 77%
315 316
O
Ph
O
O
O
Ph
Ph
O
O
O
Ph
318a 13% 318b 8% 318c 33%
In the course of the study on developing conditions for preparation of 4-alkylidene
cyclopentenones, a similar trend was observed when using Ir(I)-catalysts (Table 4.1, in Section
4.2). Subsequently, it was shown that an in situ prepared catalyst by sequential addition of PPh3
and AgBF4 to [Rh(CO)2Cl]2 exhibits remarkable reactivity in promoting the reaction with the
distal double bond of the allene (Scheme 4.50, for details see Section 4.2).
Scheme 4.50 Rh(I) catalyzed formation of 4-alkylidene cyclopentenones.
PN
MeO 2C
R 1
73
•
R 3
R 2
H
10 mol % [Rh(CO) 2Cl] 2
30 mol% PPh 3, 22 mol % AgBF 4
DCE, rt - 40 o C, 1h
P
N
MeO2C R1 R 3
R 2
O
BzN
MeO 2C
We became interested whether the double bond selectivity of this Rh(I)-catalyzed allenic
cyclocarbonylation reaction can be reversed by using diphosphine ligands. It is generally
accepted that diphosphine ligands can have a profound effect on various transition metal-
catalyzed reactions. Most often this effect is on the rate and observed yield of the reaction,
however there are some instances where ligands have affected the formation of structurally
different products. Recent reviews by van Leeuwen and coworkers have summarized and related
such effects to the natural bite angle of diphosphines. 224 One compelling example is the ligand
effect on the Pd-catalyzed hydroxycarbonylation reaction of styrene, where formation of a
130
270
R 1
74
O
•
H
H