Abstract
An efficient synthesis of hydrazones of 4-(3-oxobutyl)semicarbazides and 4-(3-oxobutyl)semicarbazones using novel semicarbazone-based amidoalkylation reagents, 1-arylidene-4-[(aryl)(tosyl)methyl]semicarbazides, has been developed. The synthesis involved reaction of the latter with the Na-enolate of acetylacetone, followed by a base-promoted retro-Claisen reaction and treatment of the obtained 4-(3-oxobutyl)semicarbazones with hydrazine or methylhydrazine. The prepared hydrazones were converted stereoselectively into 14-membered cyclic bis-semicarbazones under acidic conditions. Especially high selectivity (trans/cis⩾97:3) was observed upon the macrocyclization of 4-(3-oxobutyl)semicarbazone hydrazones. A plausible reaction pathway and the stereochemistry of this cyclization were discussed.
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