Download (3249Kb) - D-Scholarship@Pitt - University of Pittsburgh

3.3 Diversification of Cross-Conjugated Trienes via Diels-Alder Reaction
3.3.1 Intermolecular Diels-Alder Approach – First Generation Triene
Sequential Diels-Alder reactions of the amino ester trienes can quickly lead to complex
molecular scaffolds, particularly if two different dienophiles are utilized in tandem fashion.
Sequential Diels-Alder reactions of acyclic cross-conjugated trienes 125 affording functionalized
decalins 127 were initially studied by Tsuge, 86 who utilized bis-silylenolether 128, and by Fallis,
who employed monosubstituted triene 129 (Scheme 3.18). 87 However, sequential reactions of
these acyclic trienes have proven difficult to control, typically affording mixtures of
regioisomers. Moreover, preparation of the acyclic trienes is not trivial, in part due to their
instability and tendency to polymerize. 88, 89 Therefore, these compounds have seen only limited
synthetic application, despite their potential. 90
Scheme 3.18 Tandem Diels-Alder reactions of acyclic cross-conjugated trienes.
E
E
[4+2]
E
E
E
E
125 126 127
E
E
[4+2]
Acyclic cross-conjugated tetraene ([4]dendralene-130) has also been recently examined for
participation in tandem Diels-Alder reactions by Willis and coworkers (Scheme 3.19). 91 For
example, the reaction of 130 with excess N-methylmaleimide affords a mixture of mono-, di and
tri-cycloaddition products. Nevertheless, this example underlines the fact that rapid increase in
molecular complexity can be obtained via tandem cycloaddition reactions of cross-conjugated
polyenes.
46
E
E
TMSO
Ph
128
OTMS
R
129
.