The photocycloaddition of naphthoates with acetylacetone; dramatic acid promotions of product quantum yields

Abstract

. Can. J. Chem. 69, 1261Chem. 69, (1991. In acetonitrile and methanol, methyl 1-and methyl 2-naphthoate (1-and 2-NpC02CH3) underwent [2+2] photocycloaddition with acetylacetone (acacH) from a reactive species derived from the lowest spectroscopic singlet excited state to give cyclobutane derivatives such as 9 that ring-opened to afford addition products of acetyl and acetonyl moieties at the 7,8-position for 1-NpC02CH3 (2 and 3) and the 1,2-position for 2-NpC02CH3 (7). Further irradiation of 3 and 7 caused a deep-seated rearrangement of 3 to give 4 and an intramolecular addition of 7 to give the caged product 8. The photocycloaddition quantum yields were increased remarkably in the presence of a trace amount (<0.001 M) of protic acids. For example, the limiting quantum yield of 2 and 3 with Qadducrs = 0.033 (in the absence) increased to Qudducts >0.5 under comparable conditions in the presence of [H2S04] = 0.001 M, approaching the maximum asymptotically at about this concentration; the increases of the quantum yield could not be correlated with H2SO4 concentrations. The acid promotion of the product formation elevated the photocycloaddition to a significantly useful preparative reaction. The photocycloaddition of 2-NpC02CH3 was quenched by tributylamine, dimethylaniline, and methyl iodide, and could not be initiated by typical triplet sensitization. Strong fluorescence of 2-NpC02CH3 at 358 nm in CH3CN was quenched by acetylacetone, tributylamine, dimethylaniline, and methyl iodide, the last of which concurrently enhanced the phosphorescence intensity of 2-NpC02CH3. In the presence of [H2S04] >0.005 M the fluorescence intensity at 358 nm was quenched and a new fluorescence at 470 nm corresponding to protonated '~-N P C O~C H~ appeared. However, in the [H2S04] <0.002 M region, the new fluorescence was not observed, indicating that the protonation scarcely occurred. The Stem-Volmer constant, obtained by the quantum yield monitor, of the 2-NpC02CH3 photocycloaddition with acacH was more than an order of magnitude smaller than that obtained by the quenching of 2-NpC02CH3 fluorescence by acacH. The discrepancies outlined above clearly demonstrate that the reactive intermediate of the photocycloaddition is not the exciplex of the spectroscopic singlet excited species of '~-N~C O~C H~ and acacH, but one that is derived from the exciplex. It is speculated that this unknown reactive intermediate interacts with a proton to promote the photocycloaddition.Key worcls: photocycloaddition of naphthoates, photorearrangement of styryl ketones, acid catalysis of quantum yields, fluorescence of protonated naphthoates, acid enhancement of singlet quenching. 0,001 M) avec une croissance asymptotique qui atteint son maximum autour de cette valeur; on n'a pas pu Ctablir de correlation entre le rendement quantique et la concentration en H2SO4. La catalyse acide de la formation des produits a transform6 la photocycloaddition en une reaction preparative d'une grande utilitt. La photocyloaddition du 2-NpC02CH3 est dtsactivee par la tribu...

Synthesis of 3‐Oxatricyclo[7.2.0.01,5]undeca‐7,10‐dienes through Intramolecular Photocycloaddition Reactions of Alkenes to 1,8 a‐Position of Naphthalene Ring

“…Photocycloaddition reactions between naphthalene rings and alkenes are known to have five modes as shown in Scheme 1. Reaction at the 1,2‐position that have high double bond character is the most common, and is described in many reports [13–70] . Reaction at the 1,3‐position via a biradical leads to compounds having a 3‐oxatricyclo[3.3.0.0 2,8 ]oct‐3‐ene skeleton, which was also shown in our earlier extensive studies [17,44,66,67,70–74] .…”

“…Photoreactions of (E)-6 ab-af, ba-bf were also performed in a similar manner. (7), 91 (24), 108 (5), 115 (24), 128 (13), 141 (12), 165 (33), 178 (39), 191 (60), 202 (27), 215 (32), 241 (22), 254 (41), 268 (64), 280 (10), 299 (100, M + ); HRMS (EI +) calcd for C 21 H 17 NO: 299.1310, found: 299.1308. (cis-7 aa): 0.009 g, 20 % yield.…”

Organic room-temperature phosphorescence from halogen-bonded organic frameworks: hidden electronic effects in rigidified chromophores

“…2). 54–56 Compared to pristine naphthalene, which has an appreciable fluorescence quantum yield of 23% (40% triplet formation yield), 55 no emission was detected from all Br n NTE in deaerated CH 2 Cl 2 up to 0.02 M (near saturation) excited at 330 nm.…”