[4-Iodo-3-(isopropylcarbamoyl)phenoxy]acetic Acid as a Highly Reactive and Easily Separable Catalyst for the Oxidative Cleavage of Tetrahydrofuran-2-methanols to γ-Lactones

Abstract

[4-Iodo-3-(isopropylcarbamoyl)phenoxy]acetic acid was developed as a highly reactive and easily separable catalyst for the oxidative cleavage of tetrahydrofuran-2-methanols to γ-lactones in the presence of Oxone® (2KHSO5·KHSO4·K2SO4) as the co-oxidant. The reactivity of this new catalyst was considerably greater than that of our previously reported catalyst, 2-iodo-N-isopropylbenzamide. The new catalyst and product were easily separated by only liquid–liquid separation without chromatography. In addition, using a mixture of nitromethane and N,N-dimethylformamide as the solvent and heating enabled a low catalyst loading, a short reaction time, and high product yield. Oxidative cleavage using the new catalyst can be used as a practical and efficient method for synthesizing γ-lactones.

Efficient and Environmentally Benign Oxidative Cleavage of Pyrrolidine-2-methanols to γ-Lactams Using 2-Iodobenzamide as a Catalyst and Oxone

“…For the initial screening of the oxidative cleavage of azacycles, we first performed the reactions of N-carbobenzyloxy(Cbz)-L-prolinol (7a), L-prolinol (9), and N-Cbz-L-proline 10 under the reported conditions 24) for the oxidative cleavage of 4 to 5 with catalyst 6 (Chart 3). Cbz-prolinol 7a was treated with 5 mol% 6 in the presence of 4 equivalents (equiv.)…”

“…In the oxidative cleavage of tetrahydrofuran-2-methanols 4 to lactones 5 using a catalyst 6, 24) the choice of solvent is very important. Therefore, we investigated the effect of different solvents on oxidative cleavage reaction using catalyst 6 and powdered Oxone (Table 2).…”

“…The 4-benzoyloxy derivative 7k was oxidized within 24 h to afford 8k in 73% yield (entry 10). Oxidation of the benzyloxy-substituted derivative 7l produced 8l in 93% yield; however, this reaction required ditert-butyl-4-methylphenol (BHT) 24,25) to prevent the undesired C-H oxidation at the benzylic position (entry 11). Pyrrolidine-2-methanol 7m, which contained an ethoxycarbonylmethoxy group at the 4-position was oxidized to give 8m in 83% yield after 10 h (entry 12).…”

“…We previously reported the oxidative cleavage of tetrahydrofuran-2-methanols 4 to γ-lactones 5 using a catalytic amount of 2-iodobenzamide 6 in the presence of an inorganic co-oxidant, Oxone (2KHSO 5 •KHSO 4 •K 2 SO 4 ) 24) (Chart 2a). This reaction did not require the use of heavy metal reagents and proceeded smoothly under environmentally benign conditions to produce lactones in high to excellent yield.…”

Hypervalent iodine-mediated synthesis and late-stage functionalization of heterocycles

“…Later, the same group developed a new catalyst, [4-Iodo-3-(isopropylcarbamoyl)phenoxy]acetic acid for the oxidation of tetrahydrofuran-2-methanols 97 and showed its reactivity greater than the previously employed catalyst 98. 61 Scheme 23. Oxidation of tetrahydrofuran-2-methanols 97 to 99 using 100 as precatalyst.…”