Intramolecular Diels‐Alder Reaction with Furan‐Diene. Activated Allene as Dienophile in a BCD‐ring Approach to Steroids
- 1 January 1987
- journal article
- research article
- Published by Wiley in Bulletin des Sociétés Chimiques Belges
- Vol. 96 (2) , 105-113
- https://doi.org/10.1002/bscb.19870960205
Abstract
In connection with the total synthesis of corticosteroids and some triterpenoids the intramolecular Diels‐Alder reaction of furans 7 and 9, possessing an activated allene as dienophilic side chain, is investigated, and compared with the cycloaddition of the analogous α, β‐unsaturated enone 5. Differences in stereoselectivity are ascribed to the enhanced exothermicity of allene dienophiles. Observed reactivity differences and the stereochemical outcome are rationalized on the basis of an asynchronous reaction course. Most important, the allene dienophile allows for carbon elongation in β ‐position of the dienophile 5 without loss of reactivity in the cycloaddition.Keywords
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