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Oxime ethers free radicals

B. Free Radical Additions to Oximes, Oxime Ethers and Nitrones. 142... [Pg.118]

Free radical addition to oximes and oxime ethers emerged as a useful alternative to addition of organometallic reagents, particularly for intramolecular reactions. The most important advantage of free radical V5. organometallic addition is its tolerance for almost any functional group (with the exception of thiocarbonyl and iodoalkyl functions). [Pg.142]

Free radicals generated by zinc and alkyl iodides easily add to oxime ethers (e.g. 106, equation 75), providing good yield of corresponding hydroxylamines 107. This reaction has also been performed in solid-phase bound oxime ethers. ... [Pg.142]

Tin-based reagents are not always snitable owing to the toxicity of organotin derivatives and the difficulties often encountered in removing tin residues from the final product. Therefore, the same authors have carried out additional experiments with 17d and several different alkyl halides under tin-free conditions. The treatment of 16d with tert-butyldiphenylsilyl chloride (TBDPSCl) and triethylamine in the presence of silver triflate in CH2CI2 affords the bis(silyloxy)enamine 17d in 92% yield (Scheme 17). When the radical reaction was carried out with ethyl iodoacetate in the presence of 2,2 -azobis(4-methoxy-2,4-dimethylvaleronitrile) (V-70) as the initiator in CH2CI2, the oxime ether 19 was obtained in 83% yield (Scheme 17). [Pg.172]

Recently, Kim and colleagues have described a new efficient method for the preparation of a-keto esters 48 via a free-radical acylation approach using (phenylsulfonyl) methoxycarbonyl oxime ether 46 as carbonyl equivalent radical acceptor (Scheme 28). The oxime 46 was conveniently prepared from readily available methylphenylsulfonyl acetate 44 by a two-step sequence (via oxime 45) as shown in Scheme 28. Nitrosation of 44 with isoamyl nitrite in the presence of sodium methoxide gave oxime 47 in 78% yield. [Pg.178]

A free radical cyclization of oxime ethers tethered to an aldehyde has been used in the synthesis of azepine derivatives . For example, oxime ether 389 is cyclized to azepine 390 by reaction with Sml2 in HMPA and f-BuOH at —78°C (equation 170) . Similar free radical cyclization of oxime ethers can be carried out also in the presence of Bu3SnH/AIBN in benzene . Oxime 0-methyl ether 391 underwent thermal cyclization in refluxing o-dichlorobenzene (ODCB) leading to the mixture of two products 392 and 393 in ratio 69 31 in overall yield of 91% (equation 171) °. Rearrangement of oxime 0-tosylates in the presence of piperidine also leads to azepine ring formation . ... [Pg.288]

An alkyl group (primary, secondary, or tertiary) can be added to the oxime ether CHr=NOCH2Ph by treatment with the appropriate alkyl halide and an equimolar amount of bis(trimethylstannyl)benzopicolinate.483 This reaction, which is a free radical addition, is another way to extend a chain by one carbon. [Pg.935]

An asymmetric synthesis of aminocyclopentitols 134-137 has been used in the synthesis of trehazolin via free-radical cycloisomerization of enantiomerically pure, alkyne-tethered oxime ethers derived from D-mannose (Scheme 17).84 Treatment of 2,3 5,6-di-(9-isopropylidene-D-mannofuranose (128)85 with ethynylmagnesium bromide gave compound 129, which underwent sequential one-pot acid hydrolysis plus diol cleavage to give 130, oximation of which afforded the radical precursor 131, in 41% overall yield from 129. The free hydroxyl group of 131 was protected as acetate 132 and tert-butyldimethylsilyl ether 133, which were isolated as inseparable... [Pg.61]

J. Marco-Contelles, C. Destabel, P. Gallego, J. L. Chiara, and M. Bemabe, A new synthetic approach to the carbocyclic core of cyclopentane-type glycosidase inhibitors Asymmetric synthesis of amino-cyclopentitols via free radical cycloisomerization of enantiomerically pure alkyne-tethered oxime ethers derived from carbohydrates, J. Org. Chem., 61 (1996) 1354-1362. [Pg.112]

Nitrosolysis of camphor ethyl acetal with ethanolic ethyl nitrite in sulphur dioxide yields the orthoester oxime (205) which is rapidly dehydrated by excess acetal to the orthoester nitrile which then reacts with sulphur dioxide to form the ester nitrile and diethyl sulphite.Further papers in this section include the full paper on ozonolysis of silyl ethers (Vol. 5, p. 33), another synthesis of camphor-enol trimethylsilyl ether (cf. Vol. 6, p. 41)/°° the conversion of camphor oxime with Grignard reagents into the corresponding imine with no aziridine formation/° the preparation of (206) by treating bornylene with trichloroacetyl isocyanate/ the oxidation of thiocam-phor to the 5-oxide and alkylation in the presence of thallium(i) ethoxide to a/S-unsaturated sulphoxides/ and the free-radical C-3 alkylation of camphor with alkenes. " ... [Pg.41]

Up until the end of the 1980s, radical carbonylation chemistry was rarely considered to be a viable synthetic method for the preparation of carbonyl compounds. In recent years, however, a dramatic change has occurred in this picture [3]. Nowadays, carbon monoxide has gained widespread acceptance in free radical chemistry as a valuable Cl synthon [4]. Indeed, many radical methods can allow for the incorporation of carbon monoxide directly into the carbonyl portion of aldehydes, ketones, esters, amides, etc. Radical carboxylation chemistry which relies on iodine atom transfer carbonylation is an even more recent development. In terms of indirect methods, the recent emergence of a series of sulfonyl oxime ethers has provided a new and powerful radical acylation methodology and clearly demonstrates the ongoing vitality of modem free radical methods for the synthesis of carbonyl compounds. [Pg.93]

Recently the same group reported new free radical-mediated tandem reactions of oxime ethers for the synthesis of heterocycles via two C-C bond-forming... [Pg.73]

This free-radical acylation approach is extended for the synthesis of a-keto esters and ketones using phenylsulfonyl methoxycarbonyl oxime ether 5 [23] and bis-methanesulfonyl oxime ether 6, respectively (Scheme 6) [24], 5 is more reactive and effective than 2b. For instance, radical reaction of tert-butyl iodide with 5 gave tert-butyl oxime ester in 65% yield, whereas the use of 2b gave the corresponding tert-butyl oxime ether in 15% yield. In free-radical-mediated ketone synthesis via a sequential radical acylation approach, 6 is used as a carbonyl equivalent geminal radical acceptor. This method works well with primary alkyl iodides but somewhat less efficiently with secondary iodides and can be applied to prepare unsymmetrical acyclic ketones as well as cyclic ketones. It is noteworthy that stable allylic and benzylic radicals react smoothly with 6. [Pg.506]

Free-radical cyclizations in which oxime ethers behave as free-radical acceptors were first noted in the 1980s [68], and a good review of the field has been published [69]. This methodology has seen use in the field of alkaloid synthesis, and the aforementioned review nicely presents many of these accomplishments. This chapter will be restricted to studies directed toward what the author considers to be targets of reasonable structural complexity. [Pg.795]

The Keck group used a slightly different approach in a synthesis of (+)-7-deoxypancratistatin (Scheme 11) [72]. Once again 104 served as the starting material. A 3-step sequence provided 107, and an additional 6 steps afforded hydrazone-oxime ether 108. Treatment of this substrate with triphenyltin hydride gave tandem-cyclization product 110 in 78% yield. The first cyclization involves powerful methodology introduced by Kim in which a free radical adds to a hydra-... [Pg.795]

Addition-elimination sequence. Addition of a photochemically generated free radical to an electron-deficient double bond engenders different consequence depending on the structural features of the substrates. Routes to functionalized nitroalkanes" and cycloalkanone oxime ethers demonstrate the versatile method. [Pg.213]

This year sees a number of examples of the use of free radical cyclisations in the synthesis of complex carbocycles. Oxime ether 8 and acrylate 9, both derived from D-glucose, undergo... [Pg.302]


See other pages where Oxime ethers free radicals is mentioned: [Pg.54]    [Pg.108]    [Pg.150]    [Pg.520]    [Pg.289]    [Pg.503]    [Pg.796]    [Pg.113]    [Pg.254]    [Pg.149]    [Pg.263]   
See also in sourсe #XX -- [ Pg.141 , Pg.142 ]




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