Pericyclic tetraene

Baldwin and coworkers described an interesting and high-yielding pericyclic domino process, consisting of a Cope and a Diels-Alder reaction, which on thermal treatment of the tetraene 4-253 led to tricyclic compound 4-254 (Scheme 4.54) [89]. 

FIGURE 7 Pericyclic reactions in the biosynthesis of giffordene and 7-methyl-cyclooctatriene. (a) The [1.7]-hydrogen shift of the thermolabile undeca-(1,3Z,5Z,8Z)-tetraene generates undeca-(2Z,4Z,6E,8Z)-tetraene (giffordene), the major product of the brown alga G, mitchellae. (b) The thermolabile nona-(l,3Z,5Z,8E)-tetraene cyclizes at ambient temperature rapidly to 7-methylcy-cloocta-l,3,5-triene. At ambient temperature, the bicyclic isomer does not contribute to the equilibrium (requires s=80°C). 

Predict the stereochemistry of the following pericyclic reactions (al The thermal cyclization of a conjugated tetraene... 

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