摘要:
The Lewis acid-promoted Diels-Aider reaction of (E,Z,E)-trienal 1 provides not only the expected cis-fused cycloadduct 16 but also the transfused products 17 and 18. Trans-fused cycloadducts 17 and 18 are also products of the Lewis acid-promoted cyclization of (E,Z,E)-trienyl acetal 2. These products presumably derive from a stepwise cyclization pathway.