Photochemistry of N‐Phthaloylcysteine Derivatives: Multiplicity‐Directed Regioselective CH Activation

Abstract

The photochemistry of the methyl esters of N-phthaloylcysteine derivatives 1 b-5b was studied. The results are remarkable, because they prove a pronounced, multiplicity-controlled regioselectivity of the initial CH activation

Time-Resolved Spectroscopy of Sulfur- and Carboxy-Substituted N-Alkylphthalimides

“…[1,2] For 2 in deoxygenated acetonitrile, F d is`0.005, but upon acetone-sensitized excitation the quantum yield is 0.12, of which a value of 0.08 [2] is accounted for by the major photoproduct 2 a (Scheme 1). [1,2] For 2 in deoxygenated acetonitrile, F d is`0.005, but upon acetone-sensitized excitation the quantum yield is 0.12, of which a value of 0.08 [2] is accounted for by the major photoproduct 2 a (Scheme 1).…”

“…[11] Charge separation prior to cyclization was assumed to occur either upon direct irradiation of 1 ± 3 in acetonitrile or after energy transfer from triplet acetone or benzophenone, but different distributions of products were obtained for 1 and 2 in the absence and in the presence of high energy sensitizers. [1,2] The role of energy and/or electron transfer has been discussed for various systems. [26±31] Examples for electron transfer substrates include sulfur-containing amino acids, in which, in alkaline aqueous solution, transfer occurs from the sulfur atom in methionine or cysteine derivatives to the triplet state of 4-carboxybenzophenone (CB).…”

Palladium-Catalyzed Cyclization Reactions of Acetylene-Containing Amino Acids

“…In case of the oxypalladation precursors, the nitrogen atom was protected according to literature procedures [15] involving either tosylation or acylation in an aqueous medium or irradiation in a microwave in the presence of phthalic anhydride. [16] In all cases, the N-protected amino acids 13 ± 16 were obtained in good yields without loss of enantiopurity according to chiral HPLC analysis (Scheme 5). Additionally, rac-12 was converted to racemic phthalimide 17.…”

“…The combined EtOAc layers were dried (MgSO 4 ) and concentrated. After purification of the crude product by flash chromatography (ether, 5% AcOH), (S)-14 was obtained as an amorphous solid; yield: 162 mg (0.58 mmol, 73% (S)-2-(1,3-Dioxo-1,3-dihydroisoindol-2-yl)pent-4-ynoic Acid (16) To a solution of (S)-11 (500 mg, 3.76 mmol) in H 2 O (10 mL) phthalic anhydride (560 mg, 3.76 mmol) was added. The reaction mixture was irradiated in a microwave until the water was evaporated.…”

Synthesis and Modifications of Amino Acids and Peptides via Diradicals

“…In the singlet case, a rapid reverse electron transfer occurs and products are only formed from the homolytic y-hydrogen transfer. In contrast to that the triplet ion pair persists some time and a proton migration from the kinetically more acidic remote CH-position may take place [29]. If only 6-CH's are available as in the case of the phthaloyl tert-leucine ester 55, the expected pyrrolizidine 56 is formed in excellent yield (Scheme 10) [31].…”