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Scheme 4.15 Rh(I)-catalyzed allenic cyclocarbonylation reaction.
E
E
Ph Ph
Si
TMS
5 mol % [Rh(CO) 2Cl] 2
Ph Ph
Si
• CO (1 atm), toluene, 90 oC 259
76%
260
O
C 6H 13
261 (62%)
TMS
Ph
O
O
C 7H 15
O
TMS
262 (64%) 263 (43%) 264 (56%)
Importantly, even terminally disubstituted allenes reacted exclusively with the distal double bond
(264). The selectivity and reactivity for the distal double bond in the Rh(I)-catalyzed reaction
was retained in substrates containing an additional carbon in the tether, thereby allowing the
construction of seven membered rings (Scheme 4.16). Notably, formation of seven-membered
rings has not been possible via the Pauson-Khand reaction of enynes, and therefore the ability to
form the larger-size ring is attributed to the allenic moiety. The first example of seven membered
ring formation in a Co-mediated allenic Pauson-Khand reaction was reported by Cazes; however,
selectivity was accomplished with a sterically biased allene. 161 Additionally, Narasaka 166 and
Mukai 167 have reported examples of a Rh(I)-catalyzed allenic cyclocarbonylation reaction
affording seven membered rings (in Mukai’s case, the proximal allenic position is substituted
with a phenylsulfonyl group).
Scheme 4.16 Formation of bicyclo[5.3.0]decadienes via an allenic cyclocarbonylation reaction.
E
E
265
•
R
5 mol % [Rh(CO) 2Cl] 2
CO (1 atm), toluene, 90 o C
E
E
R
O
266a R = i-Pr, (76%)
266b R = Ph, (77%)
The bicyclo[5.3.0]decadiene system obtained in this manner is found in a variety of terpenoid
natural products with a broad range of biological activities. 168 Brummond and coworkers have
89
O