Development of cationic Diels-Alder reaction in highly polar media and total syntheses of natural products

Our longstanding interest in the Diels-Alder reactions led us to examine li thium perchlorate in diethyl ether (LPDE) as a medium for effecting [4 + 2] cycloadditions, despite the general view that the rate of the Diels-Alder reaction is essentially independent of solvent polarity. This article descr ibes an efficient, synthetically useful protocol for the construction carbo cyclic systems via intramolecular cationic Diels-Alder reactions of in situ -generated heteroatom-stabilized allyl cations in highly polar media. We al so present that use of catalytic acid in LPDE to promote intramolecular Die ls-Alder reactions of conformationally restricted substrates possessing ter minal dienes results in acid catalyzed migration of the diene prior to [4 2] cycloaddition.