O-Nitro-Group-Directed Selective Deacylation And Desulfonation And Preliminary Research On The Green Oxidation Of Benzyl Alcohols Using Hydrogen Peroxide Catalyzed Jointly By Iodine And Tertiary Amine Oxides

Phenolic esters are important organic intermediates. They are used in synthesizing pharmaceutical products, dyes and new materials and so on. Phenolic esters provide effective protections for phenolic hydroxyl groups. Selective deacylation and desulfonation will yield new type of esters and sulfonates. Our research has been oriented in discovering mild, selective and high yielding procedures for these types of compounds.We started from 2-nitro-1, 4-diphenolic esters using AlCl3 at 20oC in anhydrous chloroform, the substrates were selectively deacylated into 4-hydroxyl-3-nitro-phenolic esters. In the selective deacylation of 4-nitro-1, 3-diphenolic esters yielded the corresponding 3-hydroxyl-4-nitro-phenolic esters.Similarly, when we started from 2-nitro-1, 4-diphenolic sulfonates, selective desulfonation yielded the 4-hydroxyl-3-nitro-phenolic sulfonates. In the selective desulfonation of 4-nitro-1, 3-diphenolic sulfonates yielded the corresponding 3-hydroxyl-4-nitro-phenolic sulfonates. Thus a series of nitro substituted phenolic esters and sulfonates were synthesized in high yields and at high reaction rates. The structures of the products were fully characterized by1HNMR, 13CNMR, IR and ESI-MS.In most cases, the selective reaction of aliphatic esters needed 1.0-2.0 eq. of AlCl3, and took less than 10 hours at room temperature for completion. But for aromatic carboxylic esters and aromatic sulfonates, higher reaction temperatures and longer reaction times were needed. The reaction conditions were optimized according to different phenolic esters and sulfonates. By comparing the reaction rates of the deacylation and desulfonation, a general mechanism represented by desulfonation directed by the nitro group is proposed. Thus we have established a new procedure for the selective deacylation and desulfonation of polyphenolic esters directed by a nitro group. The regioselectivity is excellent and the reaction rate and yield are high. The products are useful intermediates in organic synthesis.These reactions demonstrate that a nitro group on a phenolic ester or sulfonate has a better ability to complex with AlCl3 than an isolated phenolic ester group does (Fries rearrangement). The directing effect of the o-nitro group was demonstrated for the first time in the selective deacylation and desulfonation for the excellent regioselectivities and good yields.Selective desulfonation of polyphenolic sulfonates has never been realized before. This represents the first selective desulfonation procedure of polyphenolic sulfonates. The products of the selective desulfonation are new types of compounds. The hydroxyl group is electron donating, especially under basic conditions. We speculate that this would dramatically influence the behavior of the aryl carbon and the sulfonoxy oxygen bond and find potential applications in organic synthesis. In the second part of the paper, a new green procedure of biscatalytic oxidation of benzyl alcohols by tertiary amine oxides, iodine and hydrogen peroxide was developed preliminarily. A series of benzyl alcohols were oxidated to the corresponding ketones or ethers using 0.1 eq. I2, 0.1 eq. R3NO and 1.2 eq. H2O2 in chloroform and water.Starting from a series of 1-phenylethyl alcohols, the corresponding ketones were obtained. However oxidation of 1-phenylpropyl alcohols yielded the corresponding ketones and the side product ethers were formed as well. In the oxidation of homologous compounds yielded mainly the corresponding ethers. The structures of the products were fully characterized by 1HNMR, IR and GC. The reaction conditions were optimized according to different benzyl alcohols. By comparing the reaction results of biscatalytic oxidation, a general mechanism is proposed. The results show that we have developed a new procedure on the green oxidation of benzyl alcohols using hydrogen peroxide catalyzed jointly by iodine and tertiary amine oxides. The reaction conditions are mild, the oxidant green and the yields good. This represents the first example of using aliphatic tertiary amine oxides as organocatalyst and the iodine molecule as catalyst in oxidation of alcohols.