Chemical Degradation of Lasalocid: (A) The Mannich Reaction (B) Baeyer-Villiger Oxidation of the Retro-Aldol Ketone

Article abstract of DOI:10.1002/hlca.19810640542

Under Mannich reaction conditions (diethylamine and formaldehyde in toluene under reflux) lasalocid (1) undergoes a unique transformation in which the carboxyl group is replaced by a diethylaminomethyl group.The resulting Mannich base 2 was converted back to lasalocid, proving that none of the other chemical and stereochemical features of the molecule were disturbed.Like other phenolic Mannich bases, the one derived from lasalocid readily alkylated mercaptans.The known thermal and base-induced retro-aldol degradations of the lasalocid both produce a ketone fragment 9 containing the cyclic ether units.Baeyer-Villiger oxidation of this ketone afforded a carboxylic acid fragment which still contained these ether units.The normal regiochemistry involved in oxidizing this ketone (R-CH2-CO-CHR'R'' type ) was cleanly reversed by first converting it into the hydroxymethylidene derivative 10.