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crude mixture after workup and can be easily isolated in this manner. The relative
stereochemistry of 293a was subsequently assigned by X-ray crystallography of the reduced
product (296, Scheme 4.41). Cyclopentenone 287b was also submitted to the same reaction
conditions to give a 66% yield of product 294 with identical diastereoselectivity.
A single attempt to convert 293a to pyrrole 295 using a Paal-Knorr protocol was unsuccessful. It
was reasoned that the strained nature of the product 295 was problematic and that reduction of
the double bond in 293a would alleviate some of this strain. Reduction of cyclopentenones 293a
and 294a to give single diastereomer of cyclopentanones 296 and 297, respectively, was effected
using Pd/C, H2 (Scheme 4.41). 207 The structure and relative stereochemistry of 296 was assigned
by X-ray crystallography, confirming that reduction occurred from the convex face to give the
cis-fused bicycle (Appendix E).
Scheme 4.41 Attempted pyrrole synthesis and reduction of 205a and 206a.
BzN
MeO2C Bn
H
R
O
293a, R = Me
294a, R = H
O
C 3H 7
R
with 293a
acetic acid, BnNH2 MeOH, molecular sieves
reflux, 12h
BzN
MeO2C Bn
H
N
C3H7 Bn
Pd/C, H2, MeOH, rt, 4h BzN
O
MeO2C Bn
H
O
C3H7 H
R
296, R = Me
297, R = H
295
not observed
X-ray of 296
When 297 was treated with benzylamine and AcOH in methanol in the presence of molecular
sieves at 70 °C, it afforded tricyclic N-benzyl pyrrole 298a in 90% yield (Scheme 4.42).
114