Direct Decarboxylative Allylation and Arylation of Aliphatic Carboxylic Acids Using Flavin‐Mediated Photoredox Catalysis

Abstract

We describe herein a direct decarboxylative allylation of aliphatic carboxylic acids with allylsulfones using visible light and riboflavin tetraacetate (RFTA) as photocatalyst. The reaction proceeds at room temperature tolerating a wide range of functionalities, avoiding the use of external bases or additives. Mechanistic studies support that alkyl radicals are involved in the reaction and that a true photocatalytic cycle is operating. It is proposed that the carboxylic acid is deprotonated by [RFTA]·–, and the corresponding carboxylate acts as a reductive quencher of RFTA*, which after decarboxylation produces the alkyl radical. The methodology was adapted to prepare benzothiazoles substituted at C2, by reacting some carboxylic acids with 2‐(phenylsulfonyl)benzothiazole. The number of carboxylic acids suitable for this arylation was lower than for the allylation and this different reactivity was briefly commented.

Continuous Flow-Enabled Synthesis of Bench-Stable Bicyclo[1.1.1]pentane Trifluoroborate Salts and Their Utilization in Metallaphotoredox Cross-Couplings

“…Among these coupling partners, carboxylic acids and potassium trifluoroborate salts have found extensive application because of their widespread availability, ease of preparation, and robust reactivity. However, despite these advantages, the cross-coupling of an aryl halide with either a BCP carboxylic acid or a BCP trifluoroborate salt has not been thoroughly explored. − Given the well-precedented advantages that these two substrate classes exhibit in terms of stability and reactivity, we decided to explore their potential utility as precursors to valuable aryl-bound BCP products.…”

Photo-Mediated Decarboxylative Giese-Type Reaction Using Organic Pyrimidopteridine Photoredox Catalysts

“…Purification by column chromatography (CH 2 Cl 2 /MeOH = 100:1) yielded the title compound 8bb (142 mg, 0.42 mmol, 84%) as a colorless oil. R f = 0.31 (CH 2 Cl 2 /MeOH = 100:2, KMnO 4 ); 1 (18), 206 (42), 188 (86), 179 (27), 161 (18), 151 (72), 142 (100), 133 (16), 121 (10), 115 (69), 109 (13), 107 (27), 95 (58), 93 (59); HRMS (ESI-TOF) m/z: [M + Na] + Calcd for C 19 H 30 O 5 Na 361.1990; Found 361.1990; IR (ATR, neat, cm −1 ): 3399 (w, br. ), 2980 (w), 2906 (w), 2852 (w), 1726 (m), 1448 (w), 1297 (w), 1210 (m), 1138 (m), 1027 (m), 939 (w).…”

“…(mixture of diastereomers). R f = 0.2 (n-pentane/EtOAc = 5:2, UV, KMnO 4 ); 1 (56) [M], 539 (7), 403 (100), 362 (84), 339 (18), 302 (12), 235 (15), 217 (15), 193 (16), 188 (11), 175 (71), 161 (10), 135 (46), 121 (17) Dimethyl 2-(2-Phenoxypropan-2-yl)succinate (8ja). Compound 8ja was prepared following general procedure A. Dimethyl maleate (144 mg, 1.0 mmol, 2.0 equiv.)…”

“…Purification by column chromatography (n-pentane/EtOAc = 9:1) yielded the title compound 8ja (37 mg, 0.13 mmol, 26%) as a colorless oil. R f = 0.45 (n-pentane/EtOAc = 9:1, KMnO 4 ); 1 H NMR (300 MHz, CDCl 3 ) δ 7.31 (m, 2H), 7.19 (m, 1H), 6.88 (m, 2H), 4.24 (m, 1H), 3.80 (s, 3H), 3.77 (s, 3H), 3.71 (m, 1H), 3.29 (dd, J = 17.5, 11.0 Hz, 1H), 1.55 (s, 3H), 1.26 (s, 3H); 13 C{ 1 H} NMR (75 MHz, CDCl 3 ) δ 172.7, 172.4, 152.5, 129.0, 127.6, 120.9, 118.0, 117.4, 108.5, 75.0, 52.6, 52.3, 50.8, 42.8, 28.6, 20.9; MS (EI): m/z (relative intensity) 280 (6), 249 (4), 220 (14), 188 (16), 166 (23), 161 (17), 145 (25), 134 (100), 127 (15), 119 (10), 106 (46), 95 (39), 83 (21), 77 ( 44 Dimethyl 2-(5-(2,5-Dimethylphenoxy)-2-methylpentan-2-yl)succinate (8ka). Compound 8ka was prepared following general procedure A for 48 h instead of 16 h. Dimethyl maleate (144 mg, 1.0 mmol, 2.0 equiv.)…”

“…In this context, riboflavin tetraacetate, structurally similar to pyrimidopteridines, can simultaneously act as a base and photocatalyst in decarboxylative transformations. 9,10 In the mid 1980's, Maki et al reported the synthesis and application of n-butyl pyrimidopteridine N-oxide (4c) as a photochemical stoichiometric oxidant. 32 In 2019, our group started to investigate these intriguing heterocycles with respect to their applicability as organic photoredox catalysts.…”