Dendralenes DTDA cascade

Scheme 12.10 An intra/intermolecular DTDA cascade of 3-substituted [3]dendralenes 56.

Only one study detailing DTDA reactions of the pseudo-acyclic 1,1- or 3,3-cyclo[3]dendralenes has been reported, most likely owing to the difficulties associated with DA reactions of such highly substituted dienes. The prototypical, and not yet reahzed, DTDA cascade of l,l-cyclo[3]dendralene 17 is presented in Scheme 12.12. If the first DA reaction occurs at the more sterically demanding exocyclic diene site, spiro-bicycle 65 is produced, which could react further to generate the... 

Scheme 12.15 In situ generation of a 1,4-cyclo[3]dendralene 76 and its DTDA cascade.

We conclude our section on cyclic [3]dendralenes with Meier and coworkers DTDA cascade of 1,5-dihydropentalene (109) [34] (Scheme 12.24). The sequence began with the addition of tetracyanoethylene (TCNE) to triene 109, providing the bridging tricycle 110. This was followed by a second in situ) DA reaction, to the less sterically encumbered bottom face of the diene, yielding 111 in excellent yield. To the best of our knowledge this is the only report of a bicyclic [3]dendralene undergoing multiple DA reactions. 

Scheme 12.26 The DTDA cascade of [4]dendralene (14) and NMM at ambient pressure and temperature.

Scheme 12.45 Highly selective DTDA cascades of [4]dendralenes.

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