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Notably, the allenic cyclocarbonylation reactions summarized in Tables 4.2 and 4.3
occurred with transfer of stereochemical information from the starting allenynes. For example,
allenyne 73a which was subjected to the reaction conditions as a mixture of diastereomers in 1.7
: 1 ratio, reacted to give the corresponding ratio of diastereomeric cyclopentenones 270a which
were separated by normal phase HPLC. Alternatively, the N-Cbz protected allenyne 73f (entry 5,
Table 4.3) was used as a nearly single diastereomer, and reacted to give cyclopentenone 270f as
a single diastereomer (diastereomer ratio of ~95 : 5 is obtained in the Claisen rearrangement, see
Chapter 2).
Scheme 4.20 Transfer of stereochemical information in the reaction of 73f.
Cbz
MeO 2C
N
1
2
Rh(I)L n
4
H
270f
Me
B
O
Cbz N
MeO2C Cbz
MeO 2C
Cbz
MeO 2C
N
1 2
N
1
1 2
H
H
73f-B
•
Me
• H
73f-A
2
273
H
Me
C 1-C 2
rotation
H
Rh
Me
O
L n
Cbz
MeO 2C
A: CO insertion; B: reductive elimination.
4
A
Rh(I)L nCO
N
1
2
271
CO
Rh
4
Ln H Me
The transfer of stereochemical information is a result of the axial chirality of the allene
which allows reaction to occur from only one diastereotopic face. As illustrated in Scheme 4.20,
despite the free rotation around the C1-C2 bond, oxidative addition of Rh(I) to form a [6,5]-fused
97