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Table 3.4 Diels-Alder reactions of 185.
Cbz
N
H
O
H
O
185
dienophile
toluene
Cbz
N
H
Entry / Product Dienophile Temperature / Time Yield dr a
1 / 186a b
2 / 186b c
3 / 186c c
N
N
O
O
O
O
NPh
NPh
O
O
O
O
H
O
186a-c
rt / 5 min 95% 1 : 0
rt / 6 h 95% > 10 : 1
rt / 3 h 78% > 10 : 1
Notes: a diastereomer ratio; b 1 equiv. of dienophile was used; c 1.5 equiv. of
dienophile was used;
X
X
Cbz
N
H
H
O
H
O
186b
X-ray of 186b
It should be noted that compounds 186a-c possess a steroidal-like heterocyclic skeleton, and
may therefore serve as useful biological probes. The rapid manner and selectivity by which these
scaffolds are assembled using this strategy make it attractive for generation of libraries of
compounds. Unfortunately, the low yields obtained during the synthesis of the key tricyclic
intermediate 185 from triene 111f (~15% overall) are a limiting factor in preparing a larger scale
library.
71
O
O
N
Ph