REACTIONS OF ORTHO-QUINONES WITH ETHOXYCARBONYLMETHYLENE(TRIPHENYL)-PHOSPHORANE - TRAPPING OF THE ORTHO-QUINONE METHANIDE INTERMEDIATES

The reactions of the ortho-quinones (5a-d) with the phosphorus ylide (6) afforded, besides the expected coumarin derivatives (10a-d), compounds (9d), (11b and c), (13), and (14). When the reactions between compounds (5a-d) and (6) were carried out in the presence of ethyl vinyl ether (20) the pyran derivatives (21 a, b, and d) and (22a, b, and d) were obtained as main products, by a [4 + 2] trapping process of the ortho-quinone methanide intermediates (7a, b, and d) with the dienophile (20). Similarly, the reaction between compounds (Sa) and (6) in the presence of a-methylstyrene afforded mainly the pyrans (23 I and II). Compounds (16), (19), and (24) were also prepared and studied.