title: Diels-alder adducts of 5-alkynylcyclopentadienols with tetracyanoethylene and dimethyl acetylenedicarboxylate: An X-ray crystallographic study of unexpected rearrangement products
abstract: The Diels-Alder reaction of tetracyanoethylene (TCNE) with 1, 4-diethyl-5-(trimethylsilyl)ethynyl-2,3-diphenylcyclopentadien-5-ol (3a) occurs on the hydroxyl-bearing face of the diene and yields ultimately an imino lactone (5a), whereby the hydroxyl functionality has added across an exo nitrile linkage. TCNE and 5-(trimethylsilyl)ethynyl-1,2,3,4-tetraphenylcyclopentadien-5-ol (3b) behave analogously. In contrast, the [4 + 2] adduct of 3b with dimethyl acetylenedicarboxylate (DMAD) undergoes a dramatic skeletal rearrangement to generate the 1,4-cyclohexadiene (9) in which an alkynyl ketone moiety has migrated onto an ester-bearing carbon. The molecules 5a and 9 have been characterized by X-ray crystallography, and a mechanism for the skeletal rearrangement is proposed.
authors.affiliation: Department of Chemistry, McMaster University, Hamilton, Ontario, L8S 4M1 Canada.
authors.initials: JA
authors.lastname: Dunn
authors.initials: M
authors.lastname: Stradiotto
authors.initials: MJ
authors.lastname: McGlinchey