With Collin s reagent

These olefins were transformed into unsaturated acetates by Woodward s protocol with iodine, silver acetate, and acetic acid. Saponification and subsequent oxidation of the liberated alcohols with Collin s reagent resulted in a 2 1 mixture of conjugated enones, 162 and 163, in mediocre yields (Scheme 16). The minor enone 163 was transformed into the cyanoketone 164 by 1,4-addition using... 

Oxidative decomplexation of the above described palladium alkyl or allyl complexes with Collin s reagent gave norbornenones 20 and nortricyclenones 21 in varying ratios depending on the starting material. ... 

Oxidative Decomplexation of Nortricyclenones from Palladium Complexes with Collin s Reagent General Procedure ... 

Oxidative decomplexation of palladium complexes obtained via methanol addition to norbor-nadiene with Collin s reagent [chromium(Vl)oxide-pyridine)2] leads to norbornenones 32 and nortricyclenones 33. ... 

Eremophilane sesquiterpenes are not widely distributed in Eremophila species. In fact, the only other example so far known is the aldehyde (70) which occurs in E. rotundifolia (66). The structure of 70 was deduced largely from H- and C-nmr spectral data and, the absolute, stereochemistry by correlation with eremophilone. The keto aldehyde was reduced with sodium borohydride-cerium trichloride to give a mixture of diastereomeric diols. The major compound was assigned the 9a-configuration. The derived diacetate, on treatment with lithium-diethylamine, gave mainly the 9-allylic alcohol which was oxidised to eremophilone with Collin s reagent. 

Write out the product formed when allyl alcohol is oxidized with Collins s reagent and when benzyl alcohol is oxidized with Collins s reagent. 

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). 

Alkylation of the acetylenic anion with isobutyraldehyde gave the propargylic alcohol which was then oxidized using Collin s reagent to yield the requisite ketone. 

This is followed by hydrolysi.s of the ester moieties with potassium carbonate and reesterification of the carboxy moiety with diazomethane to produce intermediate 65. The solitary free alcoholic hydroxyl at C-9 is oxidized with Collins reagent and the silyl ether groups are removed with acetic acid to give enprostil (63) [15]. 

Oxidation of a chiral alcohol. The (S -alcohol 1 is oxidized in high yield by DMSO-C5H5N SO3 to the aldehyde 2 with no more than 0.1% racemization. The same oxidation when effected with Collins reagent or with H2CrO4-Si02 (8, 110) proceeds with 5% and 22% racemization, respectively.4... 

Pyridinium Chlorochromate. The need for improved oxidation of primary alcohols and greater ease for isolation of products prompted further research into the nature of Cr(VI) reagents. Corey found that addition of pyridine to a solution of chromium trioxide in aqueous HCl allowed crystallization of a solid reagent characterized as 31, pyridinium chlorochromate (PCC). This reagent was superior for the conversion of primary alcohols to aldehydes in dichloromethane but less efficient than the Collins oxidation when applied to allylic alcohols. Oxidation of 1-heptanol with PCC in dichloromethane gave 78% of heptanal, for example. As stated by Corey, PCC is an effective oxidant in dichloromethane although aqueous chlorochromate species are not very effective oxidants. Oxidation of secondary alcohols to ketones is straightforward, as in Banwell s synthesis of y-lycorane, in which 32 was oxidized by PCC to the ketone (33). ... 

In contrast to the Collins reagent, the complex formed by 3,S-dimethylpyrazoIe with chiomium(VI) oxide (2) is very soluble in dichloromethane. Hence, reactions (up to 0.1 mol scale) can be carried out in the minimum amount of solvent. Generally, 2.5 equiv. of complex, generated in situ, gives good yields of aldehydes and ketones. In addition, upon work-up most of the chromium salts may be precipitated by dilution with diethyl ether. 

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