Strain-Activated 1,3-Butadienes. Synthesis and Dienic Reactivity of Dicyclobutylideneethane

Article abstract of DOI:10.1021/jo00219a013

A synthesis of dicyclobutylideneethane (3) is described.An approach involving 1-(trimethylsilyl)-substituted cyclobutanes was first examined and shown not to be conducive for gaining access to this strained diene.A Wittig approach involving condensation of cyclobutylideneacetaldehyde (18) with cyclobutylidenetriphenylphosphorane (20) did deliver 3, whose dienic behavior toward several dienophiles was examined.The electronic spectrum of 3 resembles that of the bicyclohexylidene analogue and its relative reactivity in a representative Diels-Alder reaction was shown to be lower than that of 1.Despite the obvious steric congestion at its bonding centers, however, 3 has reasonable reactivity.Various approaches to cyclobutylidenecyclopropylideneethane (2) have been examined without success.These efforts are briefly summarized.