With Jones reagent

Note 1. The oxidation can also be carried out with Jones reagent at 0°. 

The sisyl ether is stable to Grignard and Wittig reagents, oxidation with Jones reagent, KF/18-crown-6, CsF, and strongly acidic conditions (TsOH, HCl) that cleave most other silyl groups. It is not stable to alkyllithiums or LiAlH4. 

A cursory inspection of key intermediate 8 (see Scheme 1) reveals that it possesses both vicinal and remote stereochemical relationships. To cope with the stereochemical challenge posed by this intermediate and to enhance overall efficiency, a convergent approach featuring the union of optically active intermediates 18 and 19 was adopted. Scheme 5a illustrates the synthesis of intermediate 18. Thus, oxidative cleavage of the trisubstituted olefin of (/ )-citronellic acid benzyl ester (28) with ozone, followed by oxidative workup with Jones reagent, affords a carboxylic acid which can be oxidatively decarboxylated to 29 with lead tetraacetate and copper(n) acetate. Saponification of the benzyl ester in 29 with potassium hydroxide provides an unsaturated carboxylic acid which undergoes smooth conversion to trans iodolactone 30 on treatment with iodine in acetonitrile at -15 °C (89% yield from 29).24 The diastereoselectivity of the thermodynamically controlled iodolacto-nization reaction is approximately 20 1 in favor of the more stable trans iodolactone 30. 

The mechanism of the oxidation of tertiary cyclobutanols with Jones reagent is believed to involve the intermediate lactols (Eq. (18)) and the cleavage of the lactol to ketol and its subsequent oxidation to diketone when R1 = H157). 

Oxidation of evermicose (122) with bromine yielded a mixture of y- and <5-lactones, which was directly acetylated. Refluxing the acetate in benzene solution in the presence ofp-toluenesulfonic acid gave (176) a mixture of the unsaturated lactones 131 and 132. In related work, Ganguly and Saksena (177) obtained an enonolactone by oxidation of D-nogalose with Jones reagent, followed by -elimination promoted by piperidine. Similarly, L-no-galose gave the enantiomeric lactone. 

The synthetic sequence, which shows only the succesful solutions adopted in every step, is outlined in Scheme 13.1.11. Reaction of l Chloroadamantan-4-one (39) [15] with sodium-potassium alloy in ether gave a mixture of ketonic and hydroxylated material which upon oxidation with Jones reagent gave 7-methylenebicyclo[3.3.1]nonan-2-one (40) in 75% yield. Reduction of 40 with sodium borohydride gave the alcohol 41 which could be also obtained in better yields from l-chloroadamantan-4-one with a large excess of sodium-potassium... 

Finally, the remaining steps were accomplished by methylation of 26a with methyl fluorosulphonate in ether to give the methylammonium salt 25, reductive cleavage of the N-0 bond with LAH and oxidation of the resulting alcohol with Jones reagent. The yields of the last three steps are almost quantitative and the overall yield of the seven steps synthetic sequence leading to optically pure (+)-luciduline (1) is 33%. 

Thus, to confirm the location of the two hydroxyl groups in inumakilactone A (28), this compound was selectively acetylated, and its diacetate selectively saponificated. The thus obtained 15- and 3-monoacetates were oxidized to the corresponding ketones with Jones reagent (Scheme 3) [40],... 

Ozonolysis of 160, followed by oxidation with Jones reagent, esterification with diazomethane, reduction of the ketone with diborane... 

Because of the special structural requirements of the resin-bound substrate, this type of cleavage reaction lacks general applicability. Some of the few examples that have been reported are listed in Table 3.19. Lactones have also been obtained by acid-catalyzed lactonization of resin-bound 4-hydroxy or 3-oxiranyl carboxylic acids [399]. Treatment of polystyrene-bound cyclic acetals with Jones reagent also leads to the release of lactones into solution (Entry 5, Table 3.19). Resin-bound benzylic aryl or alkyl carbonates have been converted into esters by treatment with acyl halides and Lewis acids (Entry 6, Table 3.19). Similarly, alcohols bound to insoluble supports as benzyl ethers can be cleaved from the support and simultaneously converted into esters by treatment with acyl halides [400]. Esters have also been prepared by treatment of carboxylic acids with an excess of polystyrene-bound triazenes here, diazo-nium salts are released into solution, which serve to O-alkylate the acid (Entry 7, Table 3.19). This strategy can also be used to prepare sulfonates [401]. 

The mechanism of the oxidation of alcohols with Jones reagent is often depicted as given below.4... 

In fact, it has been reported34 that benzyl ethers can react with Jones reagent, resulting in the formation of ketones and benzoates. This happens under relatively harsh conditions, and nonnally no interference from benzyl ethers is observed during the oxidation of alcohols with Jones reagent. 

Nonnally, nitrocompounds resist57 the action of Jones reagent. Very rarely, a nitrogroup can suffer activation on contact with Jones reagent, resulting, on being attacked by a nucleophile. This reaction can compete with the normal... 

Nitrocompounds resist the action of PDC during the oxidation of alcohols.157 On rare occasions, PDC can promote the attack of nucleophiles on nitro groups, in a similar manner to the one observed with Jones reagent (see page 10). 

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