Reagents Jones

A. Ducke/Bees/ Whatever MUST keep the temperature in the range of 20 to 30 C during the dripping of the Jones Reagent. Either add tepid OR cool ice to the water bath to keep it in this range. Maintain drip at 1 large drop every 4 to 5 seconds...Quack This is imperative since the mecanism of chromic... 

Selective oxidation of secondary alcohols to ketones is usually performed with CrOj/HjSO, I I in acetone (Jones reagent) or with CrOjPyj (Collin s reagent) in the presence of acid-sensitive groups (H.G. Bosche, 1975 C. Djerassi, 1956 W.S. Allen, 1954). As mentioned above, a,)S-unsaturated secondary alcohols are selectively oxidized by MnOj (D.G. Lee, 1969 D. Arndt, 1975) or by DDQ (D. Walker, 1967 H.H. Stechl, 1975). 

When a solution of chromic and sulfuric acids in water is added at 0-20° to an alcohol or formate dissolved in acetone, a rapid oxidation takes place with the separation of the green chromium III reduction product as a separate layer. This system is commonly known as Jones reagent. The rate of oxidation is so fast that it is often possible to run the reaction as a titration to an... 

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

Secondary bicyclic alcohols are quantitatively oxidized by Jones reagent however rearranged products are obtamed [5f ] (equation 47)... 

The result of oxidation of 8-hydroxy-2,3-tetrafluorobenzobicyclo[3 2 l]octa-2,6-diene depends on the configuration of the hydroxyl group In the syn isomer, the double bond is not epoxidized by the Jones reagent [5/] (equation 52)... 

This group is stable to 3 AHCl, 100° 3 ANaOH, 100° H2, 1200 psi O3, MeOH, —78° RaNi, 100° LiAlH4 Jones reagent and pyridinium chlorochromate (PCC). It has also been used for protection of the anomeric hydroxyl during oligosaccharide synthesis. ... 

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 variety of chromium (VI) oxidizing systems have been developed which allow for the oxidation of a wide range of sensitive compounds. One of the most widely used chromium (VI) reagents is the Jones reagent (/), whose use is detailed in the procedure. A related system employs acetic acid as the solvent, and an example of this reagent is also given. 

Oxo-1 Id, 150i-bis-(tetrahydropyran-2-yloxy)-16-phenoxy-cis-5-trans-13-O -tetranorprosta-dienoic acid To a solution cooled to -10°C under nitrogen of 754 mg (1.3 mmols) 90 -hy-droxy-1 la.l 50 -bis-(tetrahydropyran-2-yloxy)-16-phenoxy-cis-5-trans-1 3-OJ-tetranorprosta-dienoic acid in 1 3 ml reagent grade acetone was added dropwise to 0.56 ml (1.41 mmols) of Jones reagent (chromic anhydride). After 20 minutes at -10°C, 0.260 ml 2-propanol was... 

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. 

With a secure route to pentacyclic amine 2, the completion of the total synthesis of 1 requires only a few functional group manipulations. When a solution of 2 in ethanol is exposed to Pd-C in an atmosphere of hydrogen, the isopropenyl double bond is saturated. When a small quantity of HCI is added to this mixture, the hydro-genolysis of the benzyl ether is accelerated dramatically, giving alcohol 15 in a yield of 96%. Oxidation of the primary alcohol in 15 with an excess of Jones reagent, followed by Fischer esterification, gives ( )-methyl homosecodaphniphyllate [( )-1] in an overall yield of 85 % from 2. 

Various experimental conditions have been used for oxidations of alcohols by Cr(VI) on a laboratory scale, and several examples are shown in Scheme 12.1. Entry 1 is an example of oxidation of a primary alcohol to an aldehyde. The propanal is distilled from the reaction mixture as oxidation proceeds, which minimizes overoxidation. For secondary alcohols, oxidation can be done by addition of an acidic aqueous solution containing chromic acid (known as Jones reagent) to an acetone solution of the alcohol. Oxidation normally occurs rapidly, and overoxidation is minimal. In acetone solution, the reduced chromium salts precipitate and the reaction solution can be decanted. Entries 2 to 4 in Scheme 12.1 are examples of this method. 

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