Imino ethers, rearrangement

The formation of tluorinated Q -hydroxy-jS-imino esters (180) by treatment of fluorinated imino ethers (179) with lithium 2,2,6,6-tetramethylpiperidide has been reported. A possible explanation for this interesting intramolecular rearrangement is proposed in Scheme 64. Acyclic imides derived from primary benzylic amines and amino acid esters have been found to undergo a novel nitrogen to carbon acyl migration via a base-generated carbanion to yield the corresponding a-amino... 

On thermolysis, appropriately substituted A-allyl-A-silyloxy enamines 19 undergo smooth [3,3]-sigmatropic rearrangements to the corresponding A-silyloxy imino ethers laP (equation 5). Two stereogenic centers are created but no reference to chiral induction is referred. High diastereoselectivity was observed and short reaction times favoured the syn A-silyloxy imino ether diastereomers. 

One of the most famous examples of intramolecular attack of oxygen on the nitriUnm ion intermediate was observed in the Beckmann rearrangement of Erythromycin oxime derivatives and was used in the discovery and synthesis of the commercial macrolide antibiotic Azithromycin 464. In fact, the Beckmann rearrangement of Erythromycin A 9( )-oxime 460 produced only small amounts (5%) of the expected amide 463, along with two isomeric imino ethers (461 and 462) in a fair yield (38 and 43%) (equation 198). 

In contrast, the isomeric Erythromycin A 9(Z)-oxime 460 produced an isomeric nitril-ium ion intermediate 465 as the result of different oxime geomehy (equation 199). In comparison with the products obtained from the ii-oxime, isomeric lactam 468 and imino ethers (466 and 467) were isolated. Reaction conditions (including solvent polarity and the concentration of the reaction mixture) proved to have a strong influence on the yields of the various products of the rearrangement. 

This mechanism is strongly supported by results from Spickett and Wright [67JCS(C)498] and Bee and Rose [66JCS(C)2031 ] In cyclizing HP by imino ethers, the [4,3-a] compound is not isolable unless R-73 = oxo otherwise it rapidly rearranges [67JCS(C)498]. 

The second arm of the scheme involves first a reaction of the (3-beta ketoester (7-1) with nitrous acid. The first product from nitrosation on the activated carbon spontaneously rearranges to afford oxime (7-2). Treatment with acetyl chloride then affords the (9-acylated oxime (7-3). Condensation of that compound with the imino ether from propionitrile leads to the formation of the imidazole (7-4). 

Photochemical Reactivity of Keto Imino Ethers Type I. Rearrangement and (2+2)-Photocycloaddition to the Carbon-Nitrogen Double Bond... 

The photoreactions of azides can in most cases be rationalized in terms of the initial formation of nitrenes which then undergo rearrangement, insertion or addition reactions. Nitrene rearrangement is thought to be responsible for the conversion of the a-azido ethers (81) into the imino ethers (82), and the first silanediimine (83) to be described has been prepared in a similar fashion from the diazide (84) as shown in Scheme 4. Intramolecular nitrene addition to suitably aligned nitrogen-nitrogen double bonds has been employed in the synthesis of triaziridines. 

The oxindole [both stereoisomers at C(7)] rearrangement products of an intermediate used previously in syntheses10 of d/e trans-heteroyohimbine types, were converted into their imino-ethers (30). A cyclization, C(16) as nucleophile... 

Isomerization. Overman rearrangement of imino ethers of glycals favors the generation of P-glycosyl amides. Interestingly, more ionic Pd species favor the a-isomers. 

This reaction was first reported by Wheeler and Johnson in 1899 and was explored extensively by Lander starting in 1900. It is a thermal conversion of alkyl imidates (also known as imino ethers ) into A -alkyl amides in the presence of an alkylting agent. Therefore, it is generally referred to as the Lander rearrangement." ... 

Reactions of Cyano- and Carboxy-thiophens.—-Amidines and imino-ethers as well as triazoles and tetrazines have been prepared from cyano-thiophens. The modified Lossen rearrangement of sodium JVA -dihydroxythiophen-2,3-di-carboxamide with benzenesulphonyl chloride furnished a mixture of (176) and (177) in 54% yield in a 1 3 ratio. Azo dyes have been prepared by diazotiza-tion of A -(4 -aminophenyl)thiophen-2-carboxamides. 2-Thienylthiocarbonyl... 

---