Synthesis of Sulfur-Containing Tricyclic Ring Systems by Means of Photoinduced Decarboxylative Cyclizations

Abstract

Keywords: Cyclic voltammetry / Cyclizations / Decarboxylations / Electron transfer / Photochemistry / Phthalimides / ThioethersThe intramolecular and intermolecular photoinduced electron transfer reactions of a series of mercaptoacetic acid and mercaptopropionic acid derivatives were investigated. In the intermolecular series, the phthalimidoalkylsulfanylalkylcarboxylates 1a−j and 2 were transformed into the tricyclic ring systems 3a−j and 4, respectively, with high regioselectivities. The mercaptoacetic acid and 2-mercaptopropionic acid derived substrates 1a−g and 2 readily cyclized in good to excellent yields (60−98%) but with low diastereoselectivities (except for 1d), whereas the corresponding 3-mercaptopropionic acid derived substrates 1h−j gave the corresponding tricyclic products 3h−j after prolonged irradiation, but with poor yields (11−20%). The intermolecular version − i.e., photodecarboxylative addition to N-methylphthalimide (5) as electron acceptor − was successful with mercaptoacetic acid, and 2-mercaptopropionic acid substrates 6a−c and the addition products 7a−c were obtained in high yields (57−90%). No ad-

Photodecarboxylation Study of Carboxy-Substituted N-Alkylphthalimides in Aqueous Solution: Time Resolved UV−Vis Spectroscopy and Conductometry

“…10 Significantly lower triplet yields were determined for 3a-c and even lower values for 1, 2a-c, and 4a-e (Table 2). Photoinduced intramolecular charge separation between the thioether and the phthalimide moieties has been proposed to account for both decarboxylation and cyclization [1][2][3][4][5][6][7][8] which may be coupled processes. The cyclization products of 1, 2, and 4 are sulfur-containing heterocycles with five-, six-, and seven-membered ring systems.…”

“…8 The equivalent conductivity of the anion (Λ ∼ 40 cm 2 Ω -1 mol -1 ) is much lower than that of OH -(Λ ) 190 cm 2 Ω -1 mol -1 ). The reason for the primary increase of ∆κ in the acidic range is likewise due to OH -formation.…”

“…12 This reaction has been applied for ω-phthalimido alkylcarboxylic acids, where numerous applications for medium and large ring synthesis were developed. 5,6,8 The photochemistry of N-phthaloylmethionine (1), 2 N-phthaloyl-S-methyl-L-cysteine (2a), 4 and of phthalimidocarboxylic compounds containing a trans-cyclohexane-1,4-diyl spacer group between the nitrogen and the carboxyl group (3a-c) 11 has recently been described in detail. For the N-phthaloylvaline methyl ester we have proposed that the formation of a photoisomer as the main product upon direct excitation occurs via an upper excited n,π * triplet state.…”

Intra‐ and Intermolecular Fluorescence Quenching of Alkylthio‐Substituted Phthalimides by Photoinduced Electron Transfer: Distance, Position and Conformational Dependence

“…Photoinduced electron transfer and subsequent proton transfer leads to triplet biradicals that combine to medium-and large-ring cycles, e. g. from the phthalimides 3-H and 5-H, respectively ( Figure 6). [22][23][24] This happens neither with the fluorescent 4,5-dimethoxy phthalimide 3 nor with the fluorescent 5, and thus, electron transfer quenching, e. g. from 3, is followed by rapid back electron transfer.…”

Photodecarboxylation of Adamantane Amino Acids Activated by Phthalimide

“…Thus, upon sensitization, δ-derivatives undergo a less efficent reaction than α-, -, or γ-derivatives. [84,85] Such a structure is not possible for the 6-E isomer. Because both diastereomers give the same product and proceed through 1-adamantyl radical in- termediate 36-Z or 36-E, the observed differences in the efficiency of the reactions are most likely from the different rates of the PET between the carboxylate and the phthalimide rather than the different rates of CO 2 elimination.…”