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cycloisomerization reactions. 40-42 Such reactions are presumed to proceed via intermediacy of
metallocyclopentenes formed by oxidative addition of the metal into the enyne. It has been
demonstrated that under an atmosphere of CO, these metallocyclopentene intermediates can be
intercepted and subsequently lead to insertion of CO in one of the metal-carbon bonds, thereby
constituting a catalytic cyclocarbonylation reaction. The first examples of late transition metal-
catalyzed cyclocarbonylations appeared in the literature in the late 1990’s. Initially, Murai 153 and
Mitsudo 154 demonstrated the use of Ru3(CO)12 under CO pressure of 10-15 atm to perform the
cycloaddition of diester-tethered substrate 232 upon heating to 140-150 °C (Scheme 4.6).
Scheme 4.6 Ru-catalyzed cyclocarbonylation reaction.
E
E
2 mol % Ru 3(CO) 12
CO(10-15 atm), 140-150 oC 1,4-dioxane 86%
E
232 233
Subsequently, in 1998, Narasaka 155 and Jeong 156 independently reported the first examples of a
Rh(I)-catalyzed cyclocarbonylation reactions. Narasaka detailed the use of the dimeric square-
planar complex [Rh(CO)2Cl]2 to catalyze the reaction of a range of substrates with catalyst
loading as low as 1 mol %. For example, the reaction of 234 proceeds at either 90 °C with 5 mol
% of catalyst or 130 °C with 1 mol %, to give cyclopentenone 235 in high yield (Scheme 4.7).
Scheme 4.7 [Rh(CO)2Cl]2-catalyzed cyclocarbonylation reported by Narasaka.
E
E
Ph
[Rh(CO) 2Cl] 2
CO(1 atm, balloon), dibutyl ether
234 235
catalyst loading temperature yield
5 mol % 90 o C 97%
1 mol % 130 o C 94%
Most importantly, with this catalyst the reaction can be carried out under 1 atm of CO by simply
using a balloon, which is in sharp contrast to many previous catalytic Pauson-Khand reactions
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E
E
E
Ph
O
O