Isomerization shifting procedure

The formation of a very electrophilic intermediate 258 from 256 and 257 is proposed (equation 78). The hydroxyl group of the oxime adds to 259, giving a reactive cationic species 260 that rearranges and affords the nitrile 261 (in the case of aldoxime, equation 79), or the amide 262 upon hydrolytic workup (equation 80). The conversion of 260 to the nitrilium ion should occur through a concerted [1,2]-intramolecular shift. This procedure can be applied in the conversion of aldoximes to nitriles. It was observed that the stereochemistry of the ketoximes has little effect on the reaction, this fact being explained by the E-Z isomerization of the oxime isomers under the reaction conditions. 

The mechanism of the catalytic cycle is outlined in Scheme 1.37 [11]. It involves the formation of a reactive 16-electron tricarbonyliron species by coordination of allyl alcohol to pentacarbonyliron and sequential loss of two carbon monoxide ligands. Oxidative addition to a Jt-allyl hydride complex with iron in the oxidation state +2, followed by reductive elimination, affords an alkene-tricarbonyliron complex. As a result of the [1, 3]-hydride shift the allyl alcohol has been converted to an enol, which is released and the catalytically active tricarbonyliron species is regenerated. This example demonstrates that oxidation and reduction steps can be merged to a one-pot procedure by transferring them into oxidative addition and reductive elimination using the transition metal as a reversible switch. Recently, this reaction has been integrated into a tandem isomerization-aldolization reaction which was applied to the synthesis of indanones and indenones [81] and for the transformation of vinylic furanoses into cydopentenones [82]. 

In a recent pubhcation the nitrile (EWG = CN) variant [ 126] of this chemistry was performed in water by applying N,N-diethylaminopropylated sihca gel as heterogeneous catalyst [ 128]. Another variant of this reaction sequence, leading to chiral sulfinylated enones, has been developed by Llera [ 129] employing the enantiomerically pure geminal bis(sulfoxide) 208 (Scheme 54). This bis(sulfoxide) was prepared from (-)-p-toluenesulfinic acid menthyl ester [100], as described by Kunieda [130]. Later this procedure was improved to increase the yield from 35 to 91% [13,131]. Treatment of 208 with enolizable aldehydes or ketones, in the presence of piperidine as a base and thiophile, initiated a reaction cascade involving a condensation step (to 210), a proton shift to allylic sulfoxide 211, and a [2,3]-0-shift followed by a piperidine-mediated desulfuration delivering the alcohols 212 as isomeric mixtures. Oxidation of the latter compounds (one of the R = H) led to enantiomerically pure E-y-oxo vinyl sulfoxides 213. 

Purely chemical processes, such as the oxidation of D-mannitol by chlorine, normally result in a mixture of D-mannose and D-fructose, but the ratio can be appreciably shifted in favor of either of these products. Indeed, prolonged treatment (3-5 days) at low temperatures gives D-mannose in good yield, whereas several short periods (1 day) afford D-fructose exclusively. After nine chlorinations of 1 day, at 4 to 20°, 53% of the hexitol is oxidized and 49% thereof is converted into D-fructose. A theoretical yield is afforded by the photochemical oxidation of D-mannitol. When a small quantity of D-fructose is added to a much greater amount of zinc oxide and exposed to the effects of air and sunlight, D-mannose and D-fructose are formed in amounts almost proportional to the amount of sunlight. It may be concluded that an effort has been made to find a cheap source for preparation of D-fructose and to lower the production costs by use of easier isolation and purification procedures. Of the various methods presented, the isomerization reaction is certainly the most promising. 

According to method A, the pure thiol (9-HS-9-BBN) is obtained from (9-H-9-BBN)2 and H2S in dried toluene at temperatures up to 100° in ibout 90% yield. The preparation of 9-HS-9-BBN from the monosulfide and HjS gas according to method B is extremely simple. No intermediate appears during the procedure. Gas is not evolved. The thiol is obtained with a yield of more than 90%. The intermediate mixtures of the monosulfide and the thiol can be analyzed semiquantitatively by B NMR measurements the signal of the monosulfide ( B, (5 84) is shifted to the signal of the thiol ( B, (5 78). Side reactions such as BC thiolyses or CgHi B isomerizations do not take place. 

At 1050, the day supervisor left the site to deal with a family medical emergency. This left no supervisor in the central control room, contrary to the operating rules. A single control room operator, very tired from 30 consecutive 12 hour shifts, was now running three operating units, including the isomerization unit as it went through its start-up procedure. 

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