Tetrahydrofuran → tert-butyl (2R)-2-ethynylpyrrolidine-1-carboxylate

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Reaction Steps

In accordance with Scheme I, N-α-t-BOC-D-proline 2a is reacted in an ether solvent such as tetrahydrofuran at a temperature ranging from -2° C. to the reflux temperature of the solvent with 10M borane-methyl sulfide complex to produce (R)-2-(hydroxymethyl)-1pyrrolidinecarboxylic acid, 1,1-dimethylethyl ester 3a. Compound 3a in a chlorinated hydrocarbon solvent such as methylene chloride is treated with an oxidizing agent such as pyridinium chlorochromate, 4Å molecular sieves and glacial acetic acid to give (R)-2-formyl-1-pyrrolidinecarboxylic acid 1,1-dimethylethyl ester 4a. Compound 4a in methylene chloride is treated with a methylene chloride solution of triphenylphosphine and carbon tetrabromide to produce (R)-2-(2,2-dibromoethenyl)-1pyrrolidinecarboxylic acid, 1,1-dimethylethyl ester 5a. The dibromo compound 5a in an ether solvent such as tetrahydrofuran is reacted at -78° C. with an alkyl lithium reagent such as sec-butyllithium to give (R)-2-ethynyl-1-pyrrolidinecarboxylic acid, 1,1-dimethylethyl ester 6a.

Provenance & Evidence