Sp-9-acetylfluorene, the initial acetylation product of 9-fluorenyllithium

The reaction of 9-fluorenyllithium with acetyl chloride (tetrahydrofuran, 2 13 K, under argon) provided four products which we have isolated and whose structures we have unequivocally identified for the first time. That of the initially formed component, 9-acetylfluorene (C15H12O), described here, sh ows it to be exclusively the sp rotamer in its crystalline form. The acetyl C-C=O plane is essentially perpendicular to the planar fluorene ring and t here is no indication of rotational restriction. In contrast, related 9-piv aloylfluorene, which we reported previously, is rotationally restricted and exists exclusively as its ap rotamer, in which the pivaloyl C-C=O plane is also almost perpendicular to the fluorene ring.