Oxidation of organic compounds with cerium(IV). XIX. Effect of alkyl substitution on the oxidative cleavage of alkylphenylmethanols

Abstract

A series of alkylphenylmethanols was oxidized with ceric ammonium nitrate (CAN) in 50% aqueous acetonitrile at Isobutyl6 15.4± 1.6 15.1 ± 0.0 55.6± 0.0 3.69 ± 0.01 Cyclopropylmethyl 14.7± 0.4 3.15± 0.46 75.5± 1.4 24.4 ± 4.1 5-Hexenyl 36.5± 1.6 13.8 ± 0.4 44.0± 0.6 3.19 ± 0.13 4-Methoxybutyl 30.8 ± 0.6 21.8 ± 0.7 47.0± 0.7 2.16± 0.07 3-Methoxypropyl 45.5 ± 3.2 24.7 ± 1.7 26.9± 2.7 1.10 ± 0.18 2-Methoxyethyl 42.1 ± 1.7 39.8 ± 0.9 19.4± 0.4 0.487 ± 0.004 4-Bromobutyl6,c 26.0± 1.0 44.0± 0.0 25.0± 2.0 0.58 ± 0.04 2-Bromoethyl" 32.0± 10.0 62.0 ± 18.0 6.4 ± 1.5 0.096 ± 0.03 2-Chloroethyl6'c 61.0± 4.0 46.0± 4.0 22.0± 2.0 0.48 ± 0.06 2-Fluoroethyl"'i 47.0 45.0 10.0 0.22 Cyclohexyl 4.46± 0.62 0.753 ± 0.027 89.6± 0.9 119.0± 2.9 Cyclopentyl 23.4± 4.0 1.16 d= 0.26 74.4± 1.2 66.1 ± 14.8 Cyclobutyl 23.0± 4.14.79 ± 0.54 6.14 ± 3.9 12.9± 1.7" In 50% aqueous acetonitrile at 80°; yields were determined by glpc using an internal standard and are based on at least three runs unless otherwise noted.6 Results based on two runs; average instead of standard deviations are presented. c Yields were determined by nmr using an internal standard.d Results based on one run.

Photocatalytic C−C Bond Cleavage and Amination of Cycloalkanols by Cerium(III) Chloride Complex

“…It is worth noting that more sterically congested substrates,such as those leading to the products 14 and 15 required longer reaction time and higher catalyst loading,thus suggesting that the ligation of the alcohol to the cerium center is crucial for this transformation. With respect to unsymmetrical substrates,ah igh degree of regioselectivity can be achieved in the CÀCbond b-scission step,asthe product derived from the most stable radical intermediate was exclusively observed in all cases (12)(13)(14)(15)(16)(17)(18). Notably,t he mild reaction conditions employed in this transformation allow expansive functionalgroup compatibility,a sd emonstrated by the highly efficient transformation of complex terpenoid-and steroid-derived cycloalkanols containing varied redox active functional groups and Lewis basic sites (14,(16)(17)(18).…”

“…[9] However,t he application of cerium(III) complexes in photoredox catalysis had not been reported until recently,a ss eminal work by Anna, Schelter, and co-workers disclosed the photoredoxmediated reductive halogen abstraction and arylation reactions by well-defined amide-and guanidinate-supported cerium(III) complexes. [10] Intrigued by the ability of alcohols to ligate to the metal center, [11] we envisioned that the resulting cerium(III) complex could be readily photoexcited by visible-light irradiation and subsequently oxidized to the Ce IV species.T he highly oxidizing Ce IV species could then promote the challenging b-scission cleavage to generate ac arbon-centered radical, [12] thus offering opportunities to install further functionality ( Figure 1).…”

Synthesis of Alkylarylcarbinols via the Reaction of Organoboranes with Arylmethyl Chlorides

“…1-Phenyl-2-methyl-1-butanol (3d). The ratio of the two diastereoisomers was 41:59, on the basis of 1 H NMR data…”

Photocatalytic C−C Bond Cleavage and Amination of Cycloalkanols by Cerium(III) Chloride Complex

“…Notably,decreasing the catalyst loading to 0.5 mol %l ed to no loss in yield when the reaction time was increased to 24 hours (entry 2). With respect to unsymmetrical substrates,ah igh degree of regioselectivity can be achieved in the CÀCbond b-scission step,asthe product derived from the most stable radical intermediate was exclusively observed in all cases (12)(13)(14)(15)(16)(17)(18). Employing tert-butylammonium salts of hydrofluorophosphate,hydroxide,acetate,and iodide instead of chloride resulted in diminished yields (entries 4-7).…”

“…Additionally,cerium-(III) compounds have long been known for their luminescence properties [8] and widely employed as activators in phosphors for solid luminescent materials. [10] Intrigued by the ability of alcohols to ligate to the metal center, [11] we envisioned that the resulting cerium(III) complex could be readily photoexcited by visible-light irradiation and subsequently oxidized to the Ce IV species.T he highly oxidizing Ce IV species could then promote the challenging b-scission cleavage to generate ac arbon-centered radical, [12] thus offering opportunities to install further functionality ( Figure 1). [10] Intrigued by the ability of alcohols to ligate to the metal center, [11] we envisioned that the resulting cerium(III) complex could be readily photoexcited by visible-light irradiation and subsequently oxidized to the Ce IV species.T he highly oxidizing Ce IV species could then promote the challenging b-scission cleavage to generate ac arbon-centered radical, [12] thus offering opportunities to install further functionality ( Figure 1).…”