Cholestanyl derivatives

Unfortunately, a large degree of anchimeric assistance does not automatically lead to a greatly reduced isotope effect. The cholesteryl derivative (45), the cholestanyl derivative (46), and the 7-norbornenyl derivative (47) show the same cc-d effect, yet (45) and (47) react with strong anchimeric assistance from the n electrons. Furthermore, (45) and (47) have greatly... 

Ethers, Esters, and Related Derivatives of Alcohols.—5a-Cholestanyl methyl ether has been cleaved inter alia) and converted into 5a-cholestanol by successive treatment with trimethylsilyl iodide and water.Pyridinium toluene-p-sulphonate has been reported as an efficient and mild catalyst for the conversion of alcohols into their tetrahydropyranyl ethers.Bile acids were efficiently performylated by treatment with 90% HCO2H-HCIO4. Selective base-catalysed... 

The alkylation reactions proceed with moderate to good yields with primary iodides (Entries 1,3,6, and 7) or bromides (Entries 2,4, and 5) in the absence of additives or polar solvents. The only byproducts detected were small amounts of ( )-a- and P-A -phthaloyl alanines and ( )-A -phthaloyl aspartic acid. In a few instances, small amounts of A Vinylphthalimide, resulting from double decarboxylation, were also detected. Shorter reaction times were required when the reaction was performed at 40 °C. Secondary iodides also gave alkylated derivatives (Entries 8 and 9). However, no alkylation was observed when more hindered substrates, such as a-cholestanyl iodide and menthyl iodide or bromide were used. These halides were recovered unchanged or suffered elimination to afford mixtures of alkenes after several days at room temperature. On the other hand, no alkylation took place with methyl p-toluenesulfonate, ethyl triflate, and propylene oxide under the same reaction conditions. Similarly, alkenyl and aiyl halides were unreactive with nickelacycles. 

Other examples of the use of this method include the preparation of tetrahydrofurfuryl bromide, 3a-cholestanyl bromide (using THF as solvent, 85% yield), and intermediates toward the syntheses of alkaloids (eqs 4 and 5). The reaction of the reagent with DMF alone generates the formamidinium salt which can ultimately result in the isolation of the formate ester derivative of the alcohol substrate (eq 6). It is therefore important that the N-halosuccinimide is added last for the preparation of alkyl halides. Other solvents used for this reaction include CH2CI2 (which can facilitate the workup of the reaction products) and HMPA. ... 

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