Oxidation ether cleavage

Oxidation of tetraethylene glycol (9) results in a 50% yield of the trioxa acid 10. Additionally 16% of the dioxa acid 11 and 3% of diglycolic acid (72) are formed by probably an oxidative ether cleavage. 

Oxidative Reactions. The majority of pesticides, or pesticide products, are susceptible to some form of attack by oxidative enzymes. For more persistent pesticides, oxidation is frequently the primary mode of metaboHsm, although there are important exceptions, eg, DDT. For less persistent pesticides, oxidation may play a relatively minor role, or be the first reaction ia a metaboHc pathway. Oxidation generally results ia degradation of the parent molecule. However, attack by certain oxidative enzymes (phenol oxidases) can result ia the condensation or polymerization of the parent molecules this phenomenon is referred to as oxidative coupling (16). Examples of some important oxidative reactions are ether cleavage, alkyl-hydroxylation, aryl-hydroxylation, AJ-dealkylation, and sulfoxidation. 

Oxidation of the alkaloid Glaucin (136) resulted in the formation of a yellow alkaloid 137, which seemingly is contained in Glaucium flavum var. vestitum (Scheme 48). Addition of methyl iodide converted this compound via a methylation/ether cleavage sequence into Corunnine (127) and small amounts of Pontevedrine (138) which is not a mesomeric betaine (71TL3093). 

Bischler-Napieralski reaction of 139 to a 3,4-dihydroisoquinoline, oxidation, dehydrogenation and reduction of the nitro to the amino function gave 140 which was subjected to a Pschorr reaction (Scheme 49). Quaternization was accomplished by methyl iodide to furnish the isoquinolininium salt 141 which underwent an ether cleavage on heating a solid sample or benzene or DMF solution to Corunnine (127) (73TL3617). 

The synthesis in Scheme 13.41 is also built on the desymmetrization concept but uses a very different intermediate. cA-5,7-Dimethylcycloheptadiene was acetoxylated with Pd(OAc)2 and the resulting all-cA-diacetate intermediate was enantioselectively hydrolyzed with a lipase to give a monoacetate that was protected as the TBDMS ether. An anti Sw2 displacement by dimethyl cuprate established the correct configuration of the C(2) methyl substituent. Oxidative ring cleavage and lactonization gave the final product. 

Alcohol ether sulfates. Ready aerobic biodegradation of AESs has been described [113], with co/(3-oxidation and cleavage of the sulfate and ether bonds attributed to the process [10]. However, molecular oxygen is not necessary for the two latter steps, and primary and ultimate degradation has been described under both aerobic and anaerobic conditions [114]. 

Ether cleavage of 4-heptyl-3-methylveratrole 121 using boron tribromide affords 4-heptyl-3-methylcatechol 122 (Scheme 38). Oxidation of the catechol 122 with o-chloranil to 4-heptyl-3-methyl-l,2-benzoquinone 123 and subsequent immediate addition of aniline leads to 5-anilino-4-heptyl-3-methyl-l,2-benzo-quinone 124. Unlike the very labile disubstituted ort/zo-quinone 123, compound 124 is stable and can be isolated. Palladium(II)-mediated oxidative cyclization of the anilino-l,2-benzoquinone 124 provides carbazoquinocin C 51. 

It is evident that some leeway is available in the substituents tolerable in the m-position. The bronchodilator sulfonterol (28) is descended from this observation. Chloromethylanisole (29) is reacted with methylmereaptan to give 30, and the newly introduced group is oxidized to the methyl-sulfonyl moiety of 31 with hydrogen peroxide. Ether cleavage, acetylation and Fries rearrangement of the phenolic acetate produces 32, which is next brominated with pyrrolidinone hydrobromide tribromide and then oxidized to the glyoxal (33) with dimethyl sulfoxide. 

Reaction of the iron complex salt 602 with the arylamine 921 in the presence of air led directly to the tricarbonyl(ri -4b,8a-dihydro-9H-carbazole)iron complex (923) by a one-pot C-C and C-N bond formation. Demetalation of complex 923 and subsequent aromatization by catalytic dehydrogenation afforded 3,4-dimethoxy-l-heptyl-2-methylcarbazole (924), a protected carbazoquinocin C. Finally, ether cleavage of 924 with boron tribromide followed by oxidation in air provided carbazoquinocin C (274) (640) (Scheme 5.120). 

As with alkenes we consider first those oxidations which do not cleave the acetylenic bond giving a-diketones, or oxidation of alkynyl amines and ethers to a-keto amides and esters, and then consider oxidative alkyne cleavage to acids. 

Asymmetric induction in cyclizution of a dienic acetal. Johnson et al reported a very high degree of asymmetric induction in the SnCl4-catalyzed cyclization of the iiL ctal I, derived from (—)-2,3-butanediol. Cyclization results in two axial ethers and two equatorial ethers cleavage and Jones oxidation converts these products into an nctuionc mixture consisting of 2a and 2b in the ratio 8 92. 

Figure 69 depicts the degradants and the proposed degradation pathway involving (1) rearrangement to isotimolol, (2) ether cleavage to form 4-hydroxy-3-morpholino-l,2,5-thiadiazole, and (3) oxidation followed by ether cleavage to form 4-hydroxy-3-morpholino-l,2,5-thiadiazole-l-oxide (109). 

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