And the Beckmann rearrangement

Zeolites have also been described as efficient catalysts for acylation,11 for the preparation of acetals,12 and proved to be useful for acetal hydrolysis13 or intramolecular lactonization of hydroxyalkanoic acids,14 to name a few examples of their application. A number of isomerizations and skeletal rearrangements promoted by these porous materials have also been reported. From these, we can underline two important industrial processes such as the isomerization of xylenes,2 and the Beckmann rearrangement of cyclohexanone oxime to e-caprolactam,15 which is an intermediate for polyamide manufacture. Other applications include the conversion of n-butane to isobutane,16 Fries rearrangement of phenyl esters,17 or the rearrangement of epoxides to carbonyl compounds.18... 

As with 1,4-oxazepines the Schmidt reaction of cyclic ketones and the Beckmann rearrangement of their oximes can be applied to the synthesis of monocyclic 1,4-thiazepines, 1,4- and 1,5-benzothiazepines and their 1-oxides and 1,1-dioxides (75CJC276). 

Both the Baeyer-Villiger and the Beckmann rearrangement are used on the cyclobutanones formed in these cycloadditions. Dechlorination of adduct 12 with zinc and rearrangement with a peroxy-acid gives a lactone 25 widely used in prostaglandin synthesis.5 Note that the more substituted carbon migrates and does so with retention of configuration. 

The most important nitrogen insertion reactions are still the Schmidt and the Beckmann rearrangements and their modifications. Yet, a number of other nitrogen insertion reactions are known, and examples will be therefore given and discussed. 

In conventional processes, hvdroxylamine preparation, oximation and the Beckmann rearrangement produce a total of up to 4.41 of ammonium sulfate per ton of caprolactam. The molar yield of lactam is around 70 per cent of theory in relation to cyclohexane, and 91 per cent in relation to phenol. With the BASF technology, only 2.61 of ammonium sulfate is produced per ton of caprolactam, and the molar yield in relation to cyclohexane is 70 per cent of theory. The use of the HPO process reduces the production of ammonium sulfate to 1.8 t per ton of caprolactam, and the molar yield is 61 per cent in relation to cyclohexane, and 93 per cent in relation to phenoL... 

Stamicarbon attempted to eliminate the co-production of ammonium sulfate completely in a variant of the HPO process, in which, during the effluent neutralization and the Beckmann rearrangement, ammonium bisulfate is formed instead of the neutral sulfate (bisulfate process). The sulfate is then pyrolysed to yield S02, nitrogen and water. The... 

Tricyclic systems which have been prepared include pyrrolo[l,2-a]thieno[3,2-/] and pyrrolo[l,2-a]thieno[3,4][l,4]diazepines <94H(38)8li>, <94jhc341> The Schmidt reaction and the Beckmann rearrangement of thieno[fc]quinolizidinones have been used for the preparation of piperidino[l,2-a][l,3] or [l,4]diazepines <94JHC49S>. 

Another prominent route to develop 1,5-difunctionlized molecular skeletons is the oxidative cleavage of cyclopentene derivatives (Scheme 2.57). In Corey s terminology of retrosynthesis this is the reconnect operation (reconnection of the two functionalities). Other reactions that faU under this heading include the Baeyer-Villiger oxidation and the Beckmann rearrangement of cyclopentanones. 

Sulphonic acids are converted to sulphonyl chlorides (4.259), and the Beckmann rearrangement of oximes can be effected (4.260). In tetrachloroethane, the pentachloride reacts with hydrazine mainly according to (4.261), but if the solvent is POCI3, the product is a linear phosphazene. 

The pentachloride is most used. It will convert snlphonic acids to snlphonyl halides (12.276), alcohols to halides (12.277) and carboxylic acids to halides (12.278). Af-alkyl-substituted amides (12.279) and ketoximes (12.280) can be converted to nitriles and the Beckmann rearrangement promoted (12.281). 

A number of syntheses of racenaic lysine (Lys, K) have been reported. However, as pointed out by Galat, with the advent of the ready availability of e-caprolactam, which can serve as a starting material, a simple method (Scheme 12.48) is derived from that lactam. Thus, as shown in Scheme 12.48, cyclohexanone was converted to the corresponding oxime and the Beckmann rearrangement was effected with sul-... 

The cyclopropenium activation approach has been employed in a number of elimination reactions, such as nucleophilic substitution of alcohol, nucleophilic acyl substitution of carboxylic acid, cyclodehydration of diol, and the Beckmann rearrangement (Scheme 6.17) [45]. 

Electronic factors provide the dominant reasons for the choice between conrotation and disrotation, and we shall consider this topic in detail in Chapter 4. However, when the choice is between the two disrotatory modes (or the two conrotatory modes), the electronic factors can still exert a profound influence, but in a rather subtle manner. Consider, for example, the disrotatory scission of the cyclopropyl cation, a species which appears to have, at best, a very transitory existence. Indeed, in most cases it appears that ring scission occurs in concerted sequence with the departure of the leaving group from the cyclopropane ring. The allyl cation is then the primary product (Equation 3.19). The participation of cr-bonds in concerted ionization-rearrangement processes is well-known, as in the pinacol-pinacolone reaction and the Beckmann rearrangement and the present case is no exception. 

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