3 4 0 2a, R= H, Y= OMe b, R= Me, Y= H 1 oxy-1, 3-butadiene (2a) under Y b (f~ d)~ catalysis led exclusively to cycloaddition at the dienophile's a,@ doublebond site and the formation of a spiro tri~ ycle.~ The absence of any adduct of the hydroanthracene type illustrated the sharp difference of reactivity of the two olefinic sites in the dien~ ne.~ This interesting result pointed to (1)(a) Publication 17 of the series" Diels-Alder Reactions of Cycloalkenones.(b) ...
