Diels-Alder reactions of the bis-diene 3 presented two opportunities of diene-dienophile pairing for conversion to an octahydronaphthalene system. In addition, each diene-dienophile pair could interact in four diastereotopic endo- and exo-bridged transition states. Upon heating in o-dichlorobenzene (reflux for 5 min), a remarkably facile cycloaddition was observed solely from the exo-bridged transition state available from conformer 12. Trans-fused ... 15 1 Finally, the synthesis ...
![6,6-dimethyl-4-methylidenebicyclo[3.1.1]heptan-7-one结构式](https://image.chemsrc.com/caspic/281/107514-23-8.png)