I am currently taking summer classes in organic chemistry 2. I am covering a uni

Question

I am currently taking summer classes in organic chemistry 2. I am covering a unit on structure and synthesis of alcohols as well as reactions of alcohols.

indolizomycin is an antibiotic that is produced by a recombinant genetic hybrid of two different strains of Streptomyces bacteria. It was first synthesized in the laboratory of S. J. Danishefsky at Yale in 1990. The final step of Danishefsky’s synthesis of racemic indolizomycin is shown below.

Paying special attention to the products, please provide a mechanism for this transformation. Assume that protons are available from the solvent. Which stereocenter in the product is undefined, i.e., could be ( R ) or ( S )?

Explanation / Answer

Since flouride ion is electronegative , it needs protons to stabilize . So it attacks on most positive center of the molecule , i.e., SiMe3 center . With its attack it leaves as Me3SiF leaving a negative charge on the carbon . To stabilise itself carbon moves its negative charge to adjacent carbon atom . Due to this movement the attacked carbon breaks the bond with oxygen molecule and forms ethene . Oxygen again moves its negative charge to its adjacent carbon forming carbon dioxide . It leaves negative charge on nitrogen atom . Nitrogen attacks nearby positive center i.e., carbon with ketonic group . This results in alcohol formation .

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