PNNL

Abstract

In this work, the biofuel target compound 2-ethyl-5,5-dimethylcyclopenta-1,3-diene (1) and its exo isomers (9a and 9b), were successfully synthesized via two different pathways from the common intermediate 4,4-dimethylcyclopent-2-ene-1-one (2). The first pathway produced the endocyclic product as a pure isomer via a triflate intermediate obtained from the ketone 2 in 60% yield, followed by copper catalyzed coupling with ethyl magnesium bromide in 63% yield. The second pathway employed a Grignard reaction with ketone 2, which generated an alcohol that was immediately subjected to mild acid catalyzed elimination upon workup of the previous step to yield a primarily a mixture of exo diastereomers 9a and 9b in 77% yield. These targets had their fuel properties characterized in a separate study.