Photolysis of triphenylcarbonium, tropylium, and triphenylcyclopropenium ion

Abstract

decomposition of solutions of 7 in organic solvents after 1 week at room temperature. Since the rearrangement of the less stable esters from other isoxazolium salts is subject to basic catalysis,218 it is also noteworthy that the N-t-butyl enol esters are not highly sensitive to base. l 4 However, these results do not establish whether the t-butyl substituent merely causes rearrangement to be extremely slow or if the enol esters are thermodynamically favored relative to the rearrangement products.The potential utility of the new esters as acylating agents was tested in a reaction of 8 with benzylamine. Equivalents of the reactants were combined in various organic solvents, and, in each case, the solvent was removed under reduced pressure the next day. Separation of the freely water-soluble by-product 9 from the residue with a few small portions of water left better than 98 % yield of pure carbobenzoxyglycylbenzylamide in each test.(14) For example, 8 was recovered in better than 90% yield after 24 hr in dry 2-picoline, (15) A portion of this investigation was carried out during the tenure of a predoctoral fellowship from the National Sir:Although the visible and ultraviolet spectra of various carbocationic species have been duly recorded and theoretically treated, the question of product formation from excited carbonium ions has been neglected. In pursuing a program concerned with photolysis of charged carbon species, we have examined the nature of the substances formed during ultraviolet irradiation of tropylium (I), triphenylcyclopropenium (11), and triphenylcarbonium (111) ions, the first carbocationic cases investigated from the standpoint of product develop-mentS2 In the first case (I), photogeneration of the [3.2.0] valence bond isomer Ia of the aromatic system "Dewar tropylium ion") apparently controls the over-all reaction course. In the other systems coupling emerges as an important p r o c e s~;~ however, depending on solvent and other factors, additional modes of reaction are also observed.aqueous sulfuric-acid for 10 min with a Hanovia 450-W high-pressure lamp (Vycor filter), 4 2 z of the tropylium ion4 (fluoroborate salt, A, , , 217 and 273 r n~)~ was consumed, giving rise to (1) For a review, see S. F. Mason, Quart. Rev. (London), 15, 335 (1961). (2) We have been able to locate in the literature only one possible prior example, the observation that 9-phenylfluorene was isolated after trityl perchlorate had lain on a desk top for 15 days [H. Dauben, Jr., J. Org. Chem., 25, 1442 (1960)J. (3) Coupling phenomena have also been encountered in anionic types: E. E. van Tamelen, J. I. Brauman, and L. E. Ellis, J. Am. Chem. SOC., 87, 4964 (1965); 89, 5073 (1967). After irradiation in 5 (4) W. von E. Doering and L. H. Knox, ibid., 76, 3203 (1954).I Ia n'v 58% yield (based on unrecovered starting material) of bicycl0[3.2.0]hepta-3,6-dien-2-01 (IV) and the corresponding ether V, colorless liquids interconvertible in dark reactions. Verification of structural assignments made initially by ir, uv, and nmr methods...

Triphenylcyclopropenium hydroxytris(pentafluorophenyl)borate salt for solvent free epoxy curing

“…Irradiation of compound 3 at 300 nm resulted in formation of hexaphenylbenzene [17,20]. The 19 F NMR analysis before irradiation show characteristic 19 F NMR spectrum for HOB(C6F5)3 -.…”

Arylallyl cations and their stereospecific cyclization to bicyclic trienylic cations

“…An example of this is the well-known conversion of triphenylmethanol into 9-phenylfluorene (16), carried out in strong acid. Photochemical cyclizations of triarylmethyl cations are also known (17). A mass-spectral study (18) of diphenylmethyl bromide has been interpreted in terms of a diphenylmethyl cation cyclization, to give an analog of VII, which subsequently loses H,.…”

The Product of Homotropylium Cation Photolysis

“…1) (1,5,6). This can be regarded as an allowed disrotatory ring closure of the C-1 and C-5 n centers of a pentadienyl cation sub-unit.…”