Intramolecular Diels-Alder reactions of the retinoid side chain

Article abstract of DOI:10.1016/0040-4020(95)00898-5

Retinyl propynyl ether (RPE) undergoes an intramolecular Diels-Alder reaction to form a tetrahydroisobenzofuran derivative by addition of the alkyne group at positions 11 and 14 of the retinoid side chain. The Diels-Alder product can be isolated after RPE has been heated in refluxing ethanol. The Diels-Alder reaction also occurs very slowly in the solid state at low temperatures. The tetrahydroisobenzofurans is readily dehydrogenated to an aromatic retinoid, a 1,3-dihydroisobenzofuran. 2-Butynyl and 2-propenyl retinyl ethers undergo intramolecular cyclization to similar Diels-Alder products that can be isolated in yields of 50-60% after the ethers have been heated in refluxing toluene.