Synthesis of Functionalized Aryloxy 1,3-Butadienes and Their Transformation to Diaryl Ethers via Diels-Alder Cycloaddition Reactions

Article abstract of DOI:10.1021/jo00124a010

The Diels-Alder reaction involving cycloaddition of aryloxy-substituted 1,3-butadienes with appropriate acetylenic electrophiles, followed by aromatization of the newly formed cyclohexadiene ring, has been used for the synthesis of diaryl ethers.The functionalized aryloxy 1,3-butadienes employed in this study were prepared by either of two methods: (1) methylenation of aryl esters via the Tebbe or related reagents, and (2) from 1-(aryloxy)-2-propanone by a sequence of formylation or alkylthio methylenation, and subsequent enolsilylation.A tetrasubstituted butadiene containing two phenoxy groups at the 1 and 3 positions also was prepared by the latter method.The cycloaddition reactions of 2,3-dioxy-substituted dienes occurred in high yield, but, as expected, with no regioselectivity to furnish nearly equal mixtures of regioisomeric cycloadducts.In contrast, application of 1,2,3-trihetero-substituted dienes resulted in regiospecific cycloaddition reactions.Transformation of the cyclohexadiene cycloadducts to an aromatic ring was accomplished by dehydrogenation with DDQ or by elimination during the cycloaddition process of a molecule of an alkyl mercaptan.A chiral acetylenic ketone derived from D- or L-serine underwent condensation, without racemization, with aryloxy dienes to provide diaryl ethers related to the isodityrosine antibiotics.