Oximes acetates

In a synthesis of sativene a carbonyl group was protected as a 2,4-DNP while a double bond was hydrated with BH3/H202/0H . Attempted protection of the carbonyl group as a ketal caused migration of the double bond protection as an oxime or oxime acetate was unsatisfactory since they would be reduced with BH3. 

Forms yellow plates from AcOH, and needles from EtOH [Slotta and Szyszke Chem Ber 68 184 7955]. With diazomethane,. 5-nitro-3,4-dimethoxyacetophenone is formed [Brady and Manjunath J Chem Soc 125 1067 1924]. The methyl ether crystallises from EtOAc or AcOH, m 88", 90-91", and the phenylhydrazone has m 108-110° (from aqueous EtOH). [Finger and Schott 7 C/icm [2] 115 288 7927.] Vor oxime m 216° (from EtOH or AcOH) and the oxime acetate has m 147° (from aq EtOH) [Vogel Monatsh Chem 20 384 1899 Brady and Dunn J Chem Soc 107 1861 7975]. 

Dibenz[c 1c ]azepine (32 a) is obtained by acid-mediated cyclization of 2 -(aminomethyl)bi-phenyl-2-carbaldehyde (31 a), which is generated in situ by reduction of the oxime acetal 30a.85 The acetyl 30 a and benzoyl 30c oximes behave similarly and give the dimethyl and diphenyl derivative 32 b and 32 c, respectively. 

Fermenting baker s yeast transformed 2-butanone oxime containing 44% excess of the ( )-isomer into optically active (R)-2-aminobutane in 58% enantiomeric excess. The chiral amine was also obtained in 24% e.e. from the oxime acetate but the oxime methyl ether gave a racemic product (equation 2)16. 

The synthesis of compounds 39, 41, and 43 by the ODPM rearrangement opens a novel photochemical route to chrysanthemic acid and other cyclopropane carboxylic acids present in pyrethrins and pyrethroids [52]. In fact, aldehyde 43 can be transformed to tran -chrysanthemic acid by simple oxidation. This new synthetic route to ecologically benign insecticides competes with the one previously described by us using the 1-ADPM rearrangement of p,y-unsaturated oxime acetates [30,53]. 

The DCA-sensitized irradiation of 107a for 13 hr affords, after column chromatography on silica gel, the rrans -cyclopropane derivative 108a (10%) as a 1 1 mixture of C=N bond fiZ-isomers. Similarly, irradiation of the oxime acetate 107b under these conditions for 2.5 hr affords, after chromatography, the rrans -cyclopropane derivative 108b (12%). These results show that the novel 1-ADPM rearrangement promoted by electron-transfer sensitization can be extended to other C—double-bond derivatives. 

In qualitative terms, the rearrangement reaction is considerably more efficient for the oxime acetate 107b than for the oxime ether 107a. As a result, the photochemical reactivity of the oxime acetates 109 and 110 was probed. Irradiation of 109 for 3 hr, under the same conditions used for 107, affords the cyclopropane 111 (25%) as a 1 2 mixture of Z.E isomers. Likewise, DCA-sensitized irradiation of 110 for 1 hr yields the cyclopropane derivative 112 (16%) and the dihydroisoxazole 113 (18%). It is unclear at this point how 113 arises in the SET-sensitized reaction of 110. However, this cyclization process is similar to that observed in our studies of the DCA-sensitized reaction of the 7,8-unsaturated oximes 114, which affords the 5,6-dihydro-4//-l,2-oxazines 115 [68]. A possible mechanism to justify the formation of 113 could involve intramolecular electrophilic addition to the alkene unit in 116 of the oxygen from the oxime localized radical-cation, followed by transfer of an acyl cation to any of the radical-anions present in the reaction medium. 

Surprisingly, 3-(2-dialkylaminoethyl)-l,2-benzisoxazoles 207 can be easily obtained by direct cyclization of the corresponding Mannich bases oxime acetates 206 in refluxing benzene in the presence of anhydrous K2CO3 (equation 90). The known methods for ring closure to 1,2-benzisoxazole were ineffective for this class of pharmacologically relevant compounds . 

The oxime acetate (217) readily undergoes electrocyclization to the dihydropyridine (218), from which pyridine is derived by loss of acetic acid. 

Glyoidonrcrile itself has not been prepared directly from acrylonitrile, but was eyatheaized recently1311 from glycidaldehyde by pyrolysis of the corresponding oxime acetate, as shown in Eq, (67). 

NX - 5-alpha-ANOROSTAN-3-ONE, 17-beta-HYDROXY-, 0-(p-NITRQPHENYL)OXIME, ACETATE (ester ... 

Steric and electronic effects on the photochemical reactivity of oxime acetates of p/y-unsaturated aldehydes. Journal of the Chemical Society, Perkin Transactions 1, 163-169 (b) Armesto, D., Horspool, W.M., Mancheno, M.J., and Ortiz, M.J. (1990) The aza-di-jt-methane rearrangement of stable derivatives of 2,2-dimethyl-4,4-diphenylbut-3-enal. Journal of the Chemical Society, Perkin Transactions... 

Acetophenone-sensitized photolysis of l-methyl-3-phenyl-2-cyclohexene-carbaldehyde oxime acetate (56) A solution of 56 (298 mg, 1.16 mmol)... 

Other cyclopropanecarboxylic acids, present in pyrethroids and of known insecticidal activity, are easily synthesized by the 1-ADPM reaction. Thus, triplet-sensitized irradiation of oxime acetates 74, 76, and 78 affords cyclopropanes 75, 77, and 79, respectively, in good yields. These photoproducts can be transformed to the corresponding carboxylic acids by using conventional routes (Sch. 33) [23]. 

A derivative of the almost fully reduced imidazo[4,5-c]pyridine ring system, 3,3a,4,5,6,7-hexa-hydro-2//-imidazo[4,5-c]pyridine (357) has been prepared (Equation (29)) <88IZV409>. Cyclization of l-hydroxy-3-hydroxyamino-2,2,6,6-tetramethyl-4-piperidone oxime acetate (356) with benz-aldehyde or formalin at — 20°C for 3 d gave the reduced bicyclic compound (357). 

A series of carbonyl reactions have been performed with l,3-dimethyl-6- and 7-carbaldehyde to give oximes, acetals, dithioacetals, and aminals as well as the hydroxymethyl derivatives on NaBH4 reduction, and the carboxylic acids on KMn04 oxidation (87JHC597). 

The conversion of steroidal ketoximes and the derived oxime acetates, benzoates and methyl and benzyl ethers into enamides was described by Barton and coworkers621,622. For example, the oxime of 5-a-cholestan-3-one (147) forms with acetic anhydride in pyridine the enamide 148 which, under the reaction conditions, is acetylated on nitrogen to form the enimide 149. Chromatography on alumina cleaves the enimide to the enamide. 

On successive treatment with trimethyloxonium tetrafluoroborate, triethylamine and aqueous acid, oxime acetate 83 prepared from cyclohexanone oxime and Ac20 yields a-acetoxy ketone 87 (Scheme 7). A similar result is obtained with other symmetric ketones including 4-heptanone, deoxybenzoin and dibenzyl ketone. 87 can also be formed by the reaction of cyclohexanone and O-acetyl-Af-methylhydroxylamine hydrochloride upon hydrolysis. If the reaction time is prolonged prior to hydrolysis, ketoamide 89 is isolated as the main product. The key step of the reaction is the [l,3]-acetoxy shift of 7V-acetoxyenamine 85 to the a-acetoxyimine 86. The formation of 89 provides support for the intermediacy of acetoxyimine 86 in the reaction sequence. The evidence available suggests that the [l,3]-acetoxy migration proceeds via a Claisen-type rearrangement (Scheme 7)78. 

Deoximiation Oximes, oximic ethers, or oxime 0-acetates can be converted into the corresponding ketones by reaction with Fe,(CO)9 in CH,OH at 60°. This reaction proceeds particularly readily and in good yield with oxime acetates. 

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