Oxone groups

This process of aging is believed to be critical in the development of delayed neuropathy, after NTE has been phosphorylated by an OP (see Chapter 10, Section 10.2.4). It is believed that most, if not all, of the B-esterases are sensitive to inhibition by OPs because they, too, have reactive serine at their active sites. It is important to emphasize that the interaction shown in Fignre 2.11 occurs with OPs that contain an oxon group. Phosphorothionates, which contain instead a thion group, do not readily interact in this way. Many OP insecticides are phosphorothionates, but these need to be converted to phosphate (oxon) forms by oxidative desulfuration before inhibition of acetylcholinesterase can proceed to any significant extent (see Section 2.3.2.2). 

Phosphorothionates OP compounds containing thion groups (cf. organophos-phates that contain oxon groups). 

Most OP pesticides are in the fourth and largest category. Many are dimethoxy or diethoxy compounds. OPs used in agriculture tend to be manufactured in the relatively stable P = S form. They are less toxic than OPs with the P = 0 (oxon) group. (Phosphates lack a sulfur atom, phos-phorothioates have a single sulfur atom, and phosphorodithioates have two sulfur atoms.) Many pesticides such as parathion, methyl parath-ion, diazinon, and chlorpyrifos are phosphoroth-ionates. 

DFP has other names (Table 57.1), although it is most commonly called diisopropylfluorophosphate or diiso-propylphosphorofluoridate, but it is also referred to as isofluorophate in some databases. It contains the oxon group (P=0) of the oxophosphates and therefore does not need a toxic activating reaction like that needed by the thiophosphates (P=S). 

Treatment of ethyl 10-methylthio-9-fluoro-3-methyl-2,3-dihydro-7-oxo-7//-pyrido[l,2,3- 7e]-l,4-benzoxazine-6-carboxylate with oxone in aqueous MeOH at 0°C afforded 10-methylsulfonyl derivative (99H(51)1563). Methylthio group in a 7-(4-methylthiophenyl)-5-oxo-2,3-dihydro-5//-pyrido[l,2,3- 7e]-l,4-benzoxazine-3-carboxamide was oxidized to a sulfoxide and a sulfone group (OOMIPl). 

Previous studies by Sorokin with iron phthalocyanine catalysts made use of oxone in the oxidation of 2,3,6-trimethylphenol [134]. Here, 4 equiv. KHSO5 were necessary to achieve full conversion. Otherwise, a hexamethyl-biphenol is observed as minor side-product. Covalently supported iron phthalocyanine complexes also showed activity in the oxidation of phenols bearing functional groups (alcohols, double bonds, benzylic, and allylic positions) [135]. Besides, silica-supported iron phthalocyanine catalysts were reported in the synthesis of menadione [136]. 

The group of Botta demonstrated the feasibility of their microwave-assisted iodi-nation protocol (see Scheme 6.143 d) toward a polymer-supported substrate [68], An appropriate pyrimidinone attached to conventional Merrifield polystyrene resin was suspended in N,N-dimethylformamide, treated with 2 equivalents of N-iodosuccini-mide (NIS), and subjected to microwave irradiation for 3 min. Treatment of the polymer-bound intermediate with OXONE released the desired 5-iodouracil in almost quantitative yield (Scheme 7.57). 

Subsequently, high chemoselectivity and enantioselectivity have been observed in the asymmetric epoxidation of a variety of conjugated enynes using fructose-derived chiral ketone as the catalyst and Oxone as the oxidant. Reported enantioselectivities range from 89% to 97%, and epoxidation occurs chemoselectively at the olefins. In contrast to certain isolated trisubstituted olefins, high enantioselectivity for trisubstituted enynes is noticeable. This may indicate that the alkyne group is beneficial for these substrates due to both electronic and steric effects. 

Although there are other convenient procedures for the conversion of sulphides into sulphoxides and sulphones, the phase-transfer catalysed reaction using Oxone has the advantage that the oxidation can be conducted in the presence of other readily oxidized groups, such as amines, alkenes, and hydroxyl groups, and acid-labile groups, such as esters and carbamates [6, 7], Hydrolysis of very acid-labile groups, such as ketals, can result in production of the keto sulphone. 

A highly selective and mild procedure for cleavage of TBDMS ethers to the corresponding alcohols by using Oxone was developed recently. Interestingly, it has been found that ferf-butyldiphenylsilyl (TBDPS) ether and certain acid-labile groups such as tetrahydropy-ranyl (THP),, V-Boc or a carbon-carbon double bond remain unaffected under the reaction... 

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