Allenes. Part XIX. Synthesis of (±)-hypoglycin A and configuration of the natural isomer
The synthesis of hypoglycin A by way of the allenic intermediate, diethyl 1-formylaminopenta-3,4-diene-1,1-dicarboxylate, by Simmons–Smith methylation, is described. Model experiments with ethyl buta-2,3-dienoate and diethyl allyl(formylamino)malonate gave ethyl methylenecyclopropanecarboxylate and, after hydrolysis and decarboxylation, 2-amino-3-cyclopropylpropionic acid. Degradation of hypoglycin A to (+)-3-methylpentanoic acid of known (S)-configuration establishes the configuration as (+)-(2S : 4S)-2-amino-4,5-methanohex-5-enoic acid.