Enol esters oxidative cleavage

Oxidative cleavage of the terminal double bond of 49 by ozonolysis to the aldehyde followed by permanganate oxidation to the acid and esterification with diazomethane produced the methyl ester 50. Dieckmann cyclisation of 50, following the procedure developed in Holton s laboratory (LDA, THF, -78 °C, 0.5 h, then HOAc, THF), gave the enol ester 5J in 93% yield (90% conversion). Decarbomethoxylation of 5J. was carried out by temporarily protection of the secondary alcohol (p-TsOH, 2-methoxypropene, 100%), and heating the resulting compound 52 with PhSK in DMF, at 86 °C (3 h) to provide 53a or, after an acidic workup, the hydroxy ketone 53b. 92% yield. 

Simple mono- or di-substituted enol ethers may be oxidized to esters and lactones (Table 8, entries 1 and 2). However, fully substituted enol ethers undergo oxidative cleavage, since the proposed mechanism for oxidation to an ester involves a hydride shift which can no longer take place. 

Since Scheme 4 implies formation of a-carbonyl radicals after deprotonation of enol radical cations, the same oxidation chemistry should potentially be accessible from various enol derivatives as enolates, silyl enol ethers and enol esters (Scheme 5). On the other hand, enol ether radical cations do not fit in this systematization since they are attacked by nucleophiles at the double bond faster than providing a-carbonyl radical intermediates through O-C bond cleavage (Sect. 4.3). 

Amino nitriles are useful for conjugate addition Acyl anion equivalents of the ester d1 synthon - C02R Methods Based on Vinyl (Enol) Ethers and Enamines Lithium derivatives of cyclic vinyl ethers The synthesis of pederin and related anti-tumour agents Lithium derivatives ofallenyl ethers Oxidative Cleavage of Allenes... 

Homoallyl bromide 314, prepared from readily available non-racemic ester 313, was converted to the Grignard reagent, which reacted with non-racemic epoxide, derived from D-maUc acid, to afford the alcohol 305. Ozonolysis of the alkene gave a ketone, which was converted into enol tri-flate 316. Ni-catalyzed cross coupling with trimethylsilylmethyl magnesium chloride afforded the allyl silane, which was converted into the allyl stan-nane 317. The asymmetric allylation of 313 with 317 provided 304 with a ration of 8.5 1. Methyl etherification and oxidative cleavage of exo-methylene... 

This disconnection suggests that 147 is prepared by enolate alkylation of cyclopentanone (Section 22.9). If a Dieckmann condensation is planned, the precursor to cyclopentanone is 148, which in turn is derived from diester 149. Another ester may be chosen at this point (methyl, etc.). Diester 149 is derived from the dicarboxylic acid, which is prepared by oxidative cleavage (ozonolysis) of cyclohexene. Bromocyclohexane 146 is now the clear precursor to cyclohexene by an E2 reaction (Chapter 12, Section 12.1). 

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