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Scheme 1.8 Examples of using a cyclocarbonylation reaction in diverse skeleton synthesis.
MeO 2C
TsN
R O 1 OR2 O
∗
34
R
Co 2(CO) 8, NMO TsN
CH 2Cl 2
Co 2(CO) 8
MeCN, DME
MeO 2C
35
R
O
R O 1 OR2 O O
36 37
Although olefins and acetylenes are most commonly utilized in carbocyclization reactions, use of
allenes as π-components is becoming increasingly prevalent. For a relatively long time since
their first synthesis, 45 allenes were considered no more than a chemical curiosity and remained
underutilized. 46 Intense research in the past decades, however, has resulted in many useful
synthetic methods involving allenes. 47, 48, 49 The two cumulated double bonds of the allene
display high reactivity towards a range of transition metals, and have been exploited in a variety
of ways. Using allenes as olefin components in transition metal-catalyzed reactions often has the
advantage of increased reactivity. This is largely due to the strain associated with having two
cumulated double bonds which is estimated at 10 kcal/mol. 50 Despite this fact, transition metal-
catalyzed carbocyclizations of allenes (e.g., cycloaddition and cycloisomerization reactions)
remain largely unexplored and underutilized in synthesis, presumably because there are no
known control elements for effecting double bond selectivity other than substrate modification. 51,
52 Recent studies by Brummond and coworkers have resulted in some of the first examples of
reagent-based control of olefin selectivity in the allenic cyclocarbonylation (Pauson-Khand
reaction) and cycloisomerization reactions. 53 Reagent-based control of double bond-selectivity in
transition metal-catalyzed carbocyclization reactions of allenes is ideally suited for application to
DOS since skeletally different products can be obtained. For example, selective engagement of
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