Selective One-Pot Synthesis of Functionalized Cyclopentenones

Double addition (1,2-1,4) of vinyl magnesium bromide to squaric acid derivatives allows the preparation of polyoxygenated cyclopentenones (8) in a one-pot procedure. The reaction occurs through the intermediate formation of octatetraenes (6). Protonation of this latter intermediate at -78 degrees C with TFE occurs selectively at the vinyl CH2 closer to the metallic centers. DFT studies of the cyclization step justify the observed distereoselectivity.