Efficient synthesis of alkynyl amides via aminocarbonylation of iodoalkynes

Abstract

Iodoethynylbenzene as iodoalkyne model compound was aminocarbonylated with tert-butylamine under carbon monoxide atmosphere in the presence of in situ palladium(0) catalysts. The formation of the unsaturated carboxamide (alkynyl amide) is always accompanied by that of the Glaser coupling product, diphenylbutadiyne. The yield of the amide-forming reaction was optimised by the systematic variation of the phosphine ligand, carbon monoxide pressure and temperature. The scope of the reaction was investigated by using various primary and secondary amines including amino acid methyl esters as N-nucleophiles.17α-(Iodoethynyl)-testosterone was also functionalised by using this methodology providing the corresponding 17α-(carboxamidoethynyl)-testosterone derivatives in up to 96% yields. The reaction was extended to 1-(iodoethynyl)cyclohex-1-ene and 1-iodohex-1-yne. Ethyl iodopropiolate gave the enamine type product by the addition of amine to the alkyne functionality which was formed from the iodoalkyne via deiodination under standard aminocarbonylation conditions. The bromo analogue, bromoethynylbenzene has shown lower reactivity than the corresponding iodo derivative.