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transformation can be regarded as Rh(I)-catalyzed substitution of an allylic amide. The related
reaction of activated allylic amines finds precedent in recent work by Lautens. 120
Scheme 3.38 Rh(I)-catalyzed rearrangement of acid 177.
Bz
N
O 2
OH
3
177
5
4
conditions A, B or C
Bz
N
H
A. 10 mol% [Rh(dppe)Cl] 2, 20 mol% AgSbF 6, DCE, 95 o C, 73%
B. 20 mol % AgSbF 6, DCE, 95 o C; no reaction
C. DCE, 95 o C; no reaction
We finally turned our attention to examining a thermal intramolecular Diels-Alder
reaction as a method for increasing molecular complexity in a diastereoselective manner. For this
purpose, tetraene 184 (Scheme 3.39) was synthesized by reduction of the methyl ester of 111f
using DIBALH, followed by condensation of the resulting alcohol with acryloyl chloride (the
low overall yield of 33% for this transformation is unoptimized).
Scheme 3.39 Synthesis of thermal Diels-Alder precursor 184.
Cbz
O
N
OMe
DIBALH (3 equiv)
CH 2Cl 2, -78 o C-rt, 65%
Cbz
OH
N
111f 183 184
O
3
2
Cl
4
5
O
O
178
Et 3N, CH 2Cl 2, rt
51%
The reactive portion of this cycloaddition precursor, a hexadienyl-acrylate, belongs to a
class of substrates whose application in synthesis remains underutilized. Recently, a
comprehensive study examined the effects contributing to the observed stereochemistry for
thermal and Lewis acid catalyzed reactions of relatively unfunctionalized hexadienyl-
acrylates. 121 In general, difficulties associated with Diels-Alder reactions of ester-tethered
substrates are attributed to existence of the ester moiety in a transoid conformation to minimize
68
Cbz
O
N
O