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eaction. 159 It was shown that Jeong’s Mo(CO)6 conditions applied to allenyne 242 containing a
terminally unsubstituted allene selectively afford the α-alkylidene cyclopentenone 243 arising
from reaction with the proximal double bond of the allene (Scheme 4.10).
Scheme 4.10 Mo(CO)6-mediated cyclocarbonylation reaction of 242.
•
TMS
Mo(CO) 6, DMSO
100 o C, toluene, 68%
242 243
Subsequent detailed studies by Brummond established that the double bond selectivity is
substrate dependent (Scheme 4.11). 160 In addition to terminally unsubstituted allenes (242),
substrates possessing one or two substituents on the terminal allenic position were found to react
selectively with the proximal double bond to give α-alkylidene cyclopentenones. In the case of
terminally monosubstituted allenes, the products are obtained as mixtures of E and Z isomers of
the exocyclic olefin. For example, reaction of allenyne 244 gives 245 as a 2 : 1 mixture of
diastereomers. The terminally disubstituted allene in 246 also reacts to give α-alkylidene
cyclopentenone 247 as a single product in 59% yield. In contrast, placing an additional
substituent on the proximal carbon of the allene as in 248, leads exclusively to formation of 4-
alkylidene cyclopentenone 249. These trends were proven general by subjecting variety of
additional substrates to the reaction conditions. 160b-c
Scheme 4.11 Mo-mediated allenic cyclocarbonylation reactions.
•
C7H15 244
•
Mo(CO) 6, DMSO
100 o C, toluene, 75%
E / Z = 2 : 1
Mo(CO) 6, DMSO
100 o C, toluene, 59%
245
246 247
O
C 7H 15
O
86
C4H9 •
248
TMS
O
Mo(CO) 6, DMSO
100 o C, toluene, 60%
C 4H 9
249
O