Photochemical Pinacol Rearrangement

Abstract

Irradiation of 9,9'-bifluorene-9,9'-diol (1) gave 9-fluorenone and spiro[9H-fluorene-9,9'(10'-H)-phenanthren]-10'-one (4), the latter arising from a pinacol rearrangement. The distribution of fluorenone and ketone 4 was solvent dependent with the latter being the major product in trifluoroethanol, a solvent known to stabilize carbocation intermediates. Laser flash photolysis of diol 1 in 2,2,2-trifluoroethanol or hexafluoro-2-propanol showed two transients absorbing at 350 and 505 nm with a weak band at 700 nm. The latter two peaks are assigned to the corresponding substituted 9-fluorenyl cation (5) formed from photoheterolysis of diol 1. Comparison of the decay kinetics between cation 5 and other 9-fluorenyl cations, the parent 9-fluorenyl and 9-phenyl-9-fluorenyl cations, showed that the decay of 5 was relatively insensitive to the nature of the solvent as compared to the latter two carbocations suggesting that unimolecular rearrangement in 5 competes with nucleophilic quenching.

Oxidative Cleavage of Alkene C=C Bonds Using a Manganese Catalyzed Oxidation with H2O2 Combined with Periodate Oxidation

“…Indeed, the outcome of the first step is not changed by the subsequent steps. To the best of our knowledge, the epoxide is not described in the literature and the diol has been shown to undergo photochemical rearrangements to the ketone and rearranged product in similar ratios to that observed here , . We surmise that the reaction either proceeds via a carbocation intermediate or formation of the diol.…”

“…To the best of our knowledge, the epoxide is not described in the literature and the diol has been shown to undergo photochemical rearrangements to the ketone and rearranged product in similar ratios to that observed here. [36,37] We surmise that the reaction either proceeds via a carbocation intermediate or formation of the diol. Although providing for facile epoxide ring opening with Fe(III) salts, the use of acetone in combination with H 2 O 2 , raises a safety issue, due to the possible formation of explosive organic peroxides.…”

Hexabenzo[4.4.4]propellane: A Helical Molecular Platform for the Construction of Electroactive Materials

“…Thus, parent propellane 3 (or structure A) was obtained in ∼60% overall yield by a reaction of 2-biphenyllithium with readily available pinacolone 1 (derived from fluorenone) followed by an acid-catalyzed Wagner−Meerwein rearrangement/cyclization of the resulting carbinol 2 (Scheme ) using a slightly modified procedure of Wittig . A similar reaction with easily available 4,4‘-di- tert -butyl-2-biphenyllithium similarly afforded di- tert -butylated derivative 5 in 75% yield.…”

Direct Transformation of Silyl Enol Ethers into Functionalized Allenes

“…[24] In addition, the antiaromatic character of the 9-fluorenyl cation in the ground state and the rigid character of the ketone-derived subunits of 8 f and 8 g are presumed to direct the course of the reaction. [25] Variation of the silyl enol ether in our new allene synthesis was studied next. Silyl enol ether 12 a was prepared from 1,3-diphenylacetone in good yield (Scheme 8).…”