Development of a General and Practical Iron Nitrate/TEMPO‐Catalyzed Aerobic Oxidation of Alcohols to Aldehydes/Ketones: Catalysis with Table Salt

Abstract

Oxidation of alcohols is a fundamental transformation related to our daily life. Traditional approaches with at least one stoichiometric amount of oxidants are expensive and cause serious environmental burdens. There are many reports on the aerobic oxidation of simple alcohols such as alkyl or phenyl carbinols and allylic alcohols, which used oxygen or air as the environmentally benign oxidant forming water as the only by-product. However, no such protocol has been reported for allenols and propargylic alcohols. Thus, it still highly desirable to develop efficient room temperature oxidations of alcohols with a wide scope including allenols and propargylic alcohols. In this paper, an efficient and clean aerobic oxidation of so far the widest spectrum of alcohols using 1 atm of oxygen or air, producing aldehydes/ketones at room temperature in fairly high isolated yields mostly within a couple of hours is described. It is interesting to observe that the reaction has been efficiently expedited by a catalytic amount of sodium chloride in easily recoverable 1,2-dichloroethane. A mechanism involving NO and NO 2 has been proposed based on the results of the control experiments and GC-MS studies of the in-situ formed gas phase of the reaction mixture.

One Pot Synthesis of γ‐Benzopyranones via Iron‐Catalyzed Aerobic Oxidation and Subsequent 4‐Dimethylaminopyridine Catalyzed 6‐endo Cyclization

“…Reactions of 1 e/2 e and1 f/2 f. UPDATES asc.wiley-vch. de 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 9,129.7,127.4,126.2,124.8,118.4,93.3,72.3,63.8,8.5,À0.5;MS (70 eV,EI) 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 3...…”

“…[8] Recently, our group developed an iron-catalyzed oxidation of different alcohols at room temperature in high yields and excellent selectivities. [9] By using this method, the oxidation of propargylic alcohols can be realized in excellent yields and selectivities. We hypothesized that by adding an extra catalyst into the oxidation system, g-benzopyranones can be generated from propargylic alcohols in a onepot process.…”

“…First, different additives were screened after the iron-catalyzed aerobic oxidation reaction. [9] When K 2 CO 3 and NaOH were used, both 2-phenyl-4H-chromen-4-one (3 a) and 2-benzylidenebenzofuran-3(2H)-one (4 a) were formed in moderate yields (Table 1, entries 1 and 2). [10] Other additive such as PCy 3 (Table 1, entry 3) resulted in a poor selectivity and low conversion.…”

Iron nitrate/TEMPO-catalyzed oxidative Passerini reaction of alcohols in air

“…Although the reaction resulted in a mixture of products, we were able to isolate the α-acyloxy-amide 4aAa in 56% yield (Scheme 2). Since Liu and Ma have reported the Fe(NO 3 ) 3 .9H 2 O/TEMPO-mediated oxidation of alcohols in DCE at room temperature, [46][47] we considered performing the same reaction in DCE. The reaction was complete in 24 h and we were pleased to observe that the isolated yield of 4aAa enhanced to 86%.…”

“…It is worth mentioning that Fe(NO 3 ) 3 .9H 2 O/TEMPO system has been reported to be excellent catalyst for the oxidation of alcohols to aldehydes under aerobic conditions. 46 …”