The product 11 has been reported earlier'* to undergo intramolecular Diels-Alder reaction leading to a mixture of 12 and 13. If 10b is heated at 180 OC for 20 h, cyclization occurs. The product (mainly one isomer) is assigned structure 14 (equatorial Me3Si) based on the assumption that the bulky Me3Si group must occupy an equatorial position in the Diels-Alder transition state 15.12 When 14 was treated with KH/HMPA, a stereo~pecific'~ Brook rearrangements led to ...
