Photodehydrocyclizations in stilbene-like compounds. X. Rearrangements in the photocyclization of 4,5-diphenyltriphenylene and 4,5-diphenylphenanthrene
We report herein the development of an acid-promoted rearrangement of oxa[4.3.2]propellanes to afford polyaromatic-fused spiro[4.5]carbocycles. DFT calculations suggest that the reaction pathway involves generation of a cyclobutyl cation, ring contraction to the cyclopropylcarbinyl cation, and dearomative ring closure by an internal 2-naphthol moiety. The resulting spirocarbocycles are synthetically
Exploiting the π-Acceptor Properties of Carbene-Stabilized Phosphorus Centered Trications [L<sub>3</sub>P] <sup>3+</sup>: Applications in Pt(II) Catalysis
Reaction of tris(dimethylaminocyclopropenium) substituted phosphine 1 with K2PtCl4 afforded the bench stable complex 3 which upon treatment with Ag[CB11H6Cl6] turned out to be an excellent catalyst for the transformation of a variety of ortho-biaryl substituted alkynes into polycyclic homo- and heteroarenes of different size, shape, and curvature through a 6-endo-dig cyclization. This constitutes the first example ever reported of using a P-1-centered trication as ligand in catalysis. The strong pi-acceptor character of 1 that derives from its three positive charges substantially increases the intrinsic pi-acidity of Pt in complex 1.PtCl2 and dramatically enhances its ability to activate pi-systems toward nucleophilic attack. As a consequence, a remarkable acceleration of the model transformation is observed when compared with other classical pi-acceptor ligands such as P(OPh)(3) or P(C6F5)(3). Moreover, the employment of 1 as ligand also expands the scope of this reaction to previously inaccessible substitution patterns. Kinetic studies and deuterium labeling experiments as well as density functional theory (DFT) calculations were performed in order to explain these findings.
Zelikovich, Lior; Hoffman, Roy E.; Ayalon , Ari, Journal of the Chemical Society. Perkin transactions II, 1992, # 10, p. 1785 - 1792
作者:Zelikovich, Lior、Hoffman, Roy E.、Ayalon , Ari、Rabinovitz, Mordecai
DOI:——
日期:——
Photodehydrocyclizations in stilbene-like compounds. X. Rearrangements in the photocyclization of 4,5-diphenyltriphenylene and 4,5-diphenylphenanthrene