The 1-Phenylsulfonylallenyl Terminus in Intramolecular Diels-Alder Reactions: Tether Length and Reactivity

All articles of this category Methods are described for the synthesis of 1-phenylsulfonylalka-1,2,( n + 4),( n + 6)-tetraenes 5 ( n = 2-4), and preliminary findings on their thermally-induced intramolecular cycloaddition behaviour are reported. The reaction of 5 ( n = 4) is slow, and engages the unactivated π-bond, whereas those of 5 ( n = 2 & 3) proceed readily and exo -selectively with dienophilic participation of the activated terminal π-bond, to give the expected [4 + 2] cycloadducts. The reactivity of 5 ( n = 2) is particularly noteworthy since cycloaddition proceeds under exceptionally mild conditions. sulfonylallene - cycloaddition - allene - IMDA