An Exceptionally Simple and Efficient Method for the Preparation of a Wide Variety of Fulvenes

Article abstract of DOI:10.1021/jo00185a001

A simple high yield method for the preparation of a wide range of structurally diverse fulvenes is described.Pyrrolidine proves to be a very effective reagent to promote fulvene formation between cyclopentadiene and a host of carbonyl compounds including simple ketones, 4-tetrahydrothiopyranone, 4-tetrahydropyranone, aldehydes bearing acidic α hydrogens, sterically encumbered aldehydes, as well as optically pure tetrahydrofuranyl aldehydes.With the exception of sterically hindered ketones such as 2,6-dimethylcyclohexanone, the reaction proceeds in acceptable to excellent yieds.The effect of variation of temperature, solvent, and concentration upon the course of the reaction was examined qualitatively.Methanol proved to be the solvent of choice.Deuterium-hydrogen exchange experiments (between MeOD, starting materials, and product) were conducted and it was found that deuterium can be encorporated both before and after fulvene formation.Epimerization of the optically pure fulvene 4 occurred to the extent of 12percent.